Illness Denial in Medical Disorders: A Systematic Review

The term “denial” has a Greek origin and derives from the word “apóphasis,” which results from the combination of “apó” meaning “away” or “far off” and “phasis” meaning “statement” or “proposition.” Consistent with the Greek origin of the term, the verb “to deny” means “to declare untrue” or “to assert the contrary of” [1]. Based on these etymological roots, attention has been initially focused on the behavioral components of denial (i.e., the direct negation of a problem in words) and the term “denial” was used essentially to refer to the conscious or unconscious tendency of some individuals to verbal repudiation or minimization of part or all of the total available meaning of an event [2, 3]. This definition relied on a psychodynamic framework, where the concept of denial, usually described as the psychological process of disavowal of reality, indicated an immature and pathological defense mechanism, mainly of patients with mental (i.e., psychotic and neurotic) disorders [4, 5]. On this background, researchers have come to conceive denial as a primitive defense, and to view its presence as a signal of serious underlying psychopathology [3]. This view of denial as a dysfunctional defense mechanism was endorsed by other psychoanalytic investigators [6‒8]. Shelp and Perl [1] noted, however, that the term “denial” and the psychoanalytic concept it represents have often been used improperly and provided a partial consideration of the complex clinical phenomena related to this construct.

It was David Mechanic [9] who linked denial to the concept of illness behavior, which refers to the ways in which given symptoms may be differentially perceived, evaluated, and acted (or not acted) upon by different kinds of persons. He noted that some individuals have the tendency to minimize symptoms, to shrug them off, and avoid seeking medical care because of their inclination to ignore illnesses [9]. Illness denial was subsequently included in Pilowsky’s [10] concept of abnormal illness behavior, which was defined as the persistence of a maladaptive mode of experiencing, perceiving, evaluating, and responding to one’s own health status, despite the fact that a doctor has provided a lucid and accurate appraisal of the situation and management to be followed (if any), with opportunities for discussion, negotiation, and clarification, based on adequate assessment of all relevant biological, psychological, social, and cultural factors. Over the years, other conceptual frameworks were used to describe the several (i.e., affective, cognitive, and interpersonal) components of illness denial and many definitions were introduced to define this construct [1, 2, 11‒20].

Fava et al. [21] developed the first diagnostic criteria for illness denial of having a physical disorder and of the need for treatment as part of the Diagnostic Criteria for Psychosomatic Research (DCPR). An updated version of these criteria was published in 2017 [22] and is displayed in Table 1. Denial was associated with characteristic health-damaging attitudes and behavior such as lack of compliance, delayed seeking of medical attention for serious and persistent symptoms, and counterphobic behavior as a reaction to the symptoms, signs, diagnosis, or medical treatment of a physical illness. Many other definitions of illness denial are available in the literature [1, 2, 12, 14, 19, 20]. The one suggested by Rainer Goldbeck [16] is very comprehensive and applies to patients with different medical conditions presenting with one or more of the following tendencies: (1) not accepting diagnosis or appearing oblivious to it; (2) minimizing the implications of their illness; (3) delay to seek medical advice; (4) refusal or poor compliance with treatment; (5) tendency to apparent detachment in the face of their illness. Thomas P. Hackett and his research group at the Massachusetts General Hospital [3, 23‒31] paved the ground for a concept of illness denial which did not necessarily involve negative outcomes and a maladaptive response to illness (e.g., delay in seeking medical help, reduced treatment compliance, and/or critical attitude toward hospital/physician) but might have an important adaptive and/or protective value, particularly in the early stages of disease, when illness denial was found to allay fear, anxiety, and other unpleasant affects.

There is thus the need for a systematic review of the literature to outline the complex manifestations of illness denial in patients with medical disorders. The major aim of this systematic review of studies was to clarify the clinical role of illness denial and its impact on a wide spectrum of health attitudes and behavior, as well as on short- and long-term outcomes in patients with different medical disorders. The multiple manifestations of denial in the setting of psychiatric disorders [32] were not included in this systematic review.

The present systematic review was conducted in accordance with the updated version of the Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) guidelines [33, 34]. The systematic search was performed in the following databases: PubMed, Scopus, and Web of Science. Each database was searched from inception to March 2023. A manual search of the literature was also performed, and reference lists of the included articles, as well as relevant review articles were examined for further studies not yet identified. Search terms were “denial,” “disease,” “disorder,” and “illness” that were combined using “AND” and “OR” as Boolean operators. A reference management software (Mendeley Desktop) was used to merge results from all searches and remove duplicates.

To be included in this systematic review, studies had to meet the following criteria: (1) English-language article published in a peer-review journal; (2) the full text of the article was available online or after request to the authors; (3) illness denial was adequately defined and appropriately evaluated with patient-reported outcome measures [35] and/or with the use of clinician-rated instruments, including open-ended questions; (4) the article was an original investigation reporting quantitative data on illness denial in a clinical population of adult patients (i.e., older than 18 years) with medical disorders (e.g., acute coronary syndrome, diabetes, cancer). Single case reports, general population studies or those where qualitative data were only available (e.g., commentaries, opinion articles), as well as studies involving pediatric or adolescent populations were excluded. Neurological and psychiatric investigations (for instance, those involving Alzheimer’s disease and/or psychotic patients) were also excluded, since they might reflect the spurious effects of lack of insight, as the result of the disease (i.e., neurodegenerative or psychopathological) process. Neuropsychological studies on anosognosia, a term originally coined by Babinski [36] to describe organically based forms of unawareness affecting patients with localized or diffuse brain damage, were also excluded. There were no restrictions regarding the year of publication and the study design.

Two authors (C.P. and D.C.) independently performed the search, screened titles, and abstracts for inclusion, evaluated the full text of articles appearing potentially relevant, selected studies meeting the eligibility criteria, and extracted data on illness denial. In case of disagreement, a consensus was reached through discussion with the senior author (G.A.F.). Data that are concerned with illness denial as a clinical factor affecting health attitudes and behavior in patients with different medical disorders, as well as those regarding the prevalence and impact of illness denial on several clinical outcomes, were extracted, analyzed, and discussed.

The initial search of the literature yielded a total of 14,098 articles, of which 2,600 on PubMed, 8,590 on Scopus, and 2,908 on Web of Science. After removing 6,743 duplicates using the reference management software, the remaining 7,355 articles were screened for evaluation. Excluding 4,638 records on the basis of title and abstract, the full text of the remaining 2,717 articles was assessed for potential inclusion. By removing a total of 2,541 records on the basis of eligibility criteria, 176 research studies were included in this systematic review. The selection/screening process of studies is described in detail in the PRISMA flowchart (shown in online suppl. Fig. S1; for all online suppl. material, see https://doi.org/10.1159/000531260). The results are presented according to manifestations of illness denial in different medical settings. Each section is subdivided according to its relationships with other health attitudes and behavior, prevalence, and clinical implications. The main characteristics (e.g., medical diagnosis, number of participants, methods of assessment of illness denial) of included studies are provided in the online supplementary material (online suppl. Table S1).

In evaluating the way in which patients with a diagnosis of acute myocardial infarction responded to symptoms of chest pain, Olin and Hackett [30] showed that the most common initial response was illness denial associated with the tendency to delay seeking medical help. In a subsequent study involving patients with a diagnosis of suspected or proved acute myocardial infarction, Hackett and Cassem [27] did not find a statistically significant relationship between illness denial and the tendency to delay seeking medical care. They showed that patients who denied minimally did not require outside help to seek medical attention [27]. Only patients with major denial (i.e., those who stated unequivocally that they felt no fear at any time throughout their hospitalization) had the tendency to delay seeking medical help unless someone else forced them into action [27]. A more recent study supported these findings showing that myocardial infarction patients with illness denial exhibited only minimally longer overall delay times to reach the coronary care unit compared to myocardial infarction patients without illness denial [37]. Different results were, however, obtained in other studies [38‒42]. In a clinical investigation involving consecutive patients with a diagnosis of acute myocardial infarction or coronary artery bypass surgery, Ades et al. [43] observed that those assessed by clinicians as denying the severity of their illness were significantly less likely to enter the cardiac rehabilitation program. In a study with myocardial infarction patients, O’Carroll et al. [40] demonstrated that those who waited over 4 h prior to seeking medical help had significantly higher levels of illness denial. Similarly, in a cross-sectional investigation examining patients with a first-time myocardial infarction, Stenström et al. [42] found that those with illness denial were more likely to delay seeking medical help and not to attend a cardiac rehabilitation program. In another cross-sectional study with acute coronary syndrome patients, Perkins-Porras et al. [41] showed that those who had greater levels of illness denial were more likely to have long pre-hospital delay (i.e., defined as the interval between symptom onset and the time of hospital admission recorded in the patients’ medical records). Other studies were concerned with the relationship between illness denial and treatment adherence [44, 45]. White et al. [45] conducted a cross-sectional study with congenital heart disease patients and found that illness denial was a significant predictor of nonadherence to cardiac care follow-up. Ganasegeran and Rashid [44] reported similar results in a cross-sectional study with post-myocardial infarction patients demonstrating that a 1-unit increase in the illness denial score was associated with a 20% increase in the odds of being non-adherent to medications.

Prevalence rates of illness denial according to DCPR criteria are reported in Table 2 [46‒49]. They ranged from 3.3% in patients with first myocardial infarction to 23.9% in those with suspected vasovagal syncope [48, 49]. Two studies estimated the prevalence rates of illness denial in cardiology with other assessment methods [45, 50]. White et al. [45] showed that a large percentage of patients (42.5%) with congenital heart disease had illness denial. Hoschar et al. [50] found that more than half (i.e., 53.2%) of patients with acute myocardial infarction exhibited illness denial in the prodromal phase of the disease.

Olin and Hackett [30] found that the majority of acute myocardial infarction patients with illness denial were aware of the seriousness of their condition but none of them showed signs of severe anxiety during the interview. A number of studies reported similar results [25, 51, 52]. Gentry et al. [52] and Froese et al. [25] showed that myocardial infarction patients with illness denial experienced less situational anxiety than did those without illness denial. Similarly, Fang et al. [37] demonstrated that patients with higher illness denial were not only less likely to suffer from anxiety and depression but they were also more likely to report optimal levels of psychological well-being in the 6 months prior to the onset of an ST-segment elevation myocardial infarction. In a study involving patients with a diagnosis of acute myocardial infarction, Havik and Mæland [53] consistently found that illness denial was significantly correlated to optimal health attitudes (i.e., more positive views of the consequences of the myocardial infarction, lower levels of hopelessness, and greater satisfaction with the hospital staff). In another study, a negative relationship between illness denial and mortality was found [26]. Illness denial was also found to predict favorable outcomes in patients with cardiovascular disorders [54‒58]. In a longitudinal study investigating the relationship between illness denial and the course of recovery in patients who were hospitalized for myocardial infarction or for coronary bypass surgery, Levine et al. [57] found that those with higher levels of illness denial spent fewer days in the intensive care unit and had fewer signs of cardiac dysfunction during their hospitalization compared to patients with lower levels of illness denial. The authors also found that, in the year following discharge, patients with higher levels of illness denial were more noncompliant with medical recommendations and required more days of rehospitalization than those with lower levels of illness denial [57]. Levenson et al. [56] showed that, compared to patients with unstable angina without illness denial, those with high levels of illness denial had half as many episodes of angina during hospitalization and were more likely to reach medical stabilization. In a longitudinal study with a follow-up period of 12 months, Julkunen and Saarinen [59] found that illness denial was a significant predictor of good recovery (i.e., return to work and self-rated health status) in myocardial infarction patients.

Pilowsky and Spence [60] were among the first to show that illness denial was a common coping strategy for patients with chronic pain, particularly for those who minimized the seriousness of their condition and also tended not to feel sad, anxious, or irritable despite the fact that their pain has persisted on average for over 10 years. In a study with chronic low back pain patients, Turner and Clancy [61] found that the denial of pain was significantly and positively correlated to downtime, meaning that those who reported greater use of illness denial spent more time lying down or in a reclining position during the day and evening. High denial was found to be associated not only with lower distress but also with reduced risk of maladaptive cognitions that can have a negative impact on patients’ adherence and response to treatment [62]. Mann et al. [63] showed that patients with chronic pain with neuropathic characteristics used illness denial as a coping strategy to reduce the emotional impact of chronic pain.

In a study including patients with pain-prone disorder (defined as persistent/continuous pain associated with a desire for surgery), Blumer and Heilbronn [64] showed that 52% of them denied having had any emotional difficulties because of their condition. In a subsequent study involving consecutive patients with chronic pain, Bouckoms et al. [65] found that the denial of feelings about suffering was documented in 44% of the sample. Holmes et al. [66] found that illness denial was present in 10 of 31 chronic pain patients (32%) with intractable nonmalignant pain.

In patients with chronic pain, Osborne and Swenson [67] found that those with high levels of muscle tension were more likely to use illness denial. Exploring whether coping strategies predicted adjustment in patients with chronic low back pain, higher scores on the subscales of denial of pain, and persistence (reflecting the patients’ tendency to ignore their pain sensations and continue, where possible, with their normal everyday functioning) were found to be associated with lower levels of disability [68].

Goldsmith et al. [69] observed attitudes of denial in psoriatic patients who were generally uncooperative in following an outpatient treatment regimen. In a subsequent cross-sectional study with patients having a dermatologist-confirmed diagnosis of psoriasis, Fortune et al. [70] found that those who used alcohol and drugs as a way of coping with their illness were more likely to be in denial and to report greater disability as a result of their psoriasis.

Using the DCPR, illness denial was detected in 10 of the 545 patients (1.8%) with various forms of skin disease undergoing a comprehensive psychosomatic assessment [71] and thus found to be relatively uncommon compared to other medical disorders (Table 2).

In patients with psoriasis, Cvitanović and Jančić [72] found that illness denial was significantly correlated with higher levels of stress and greater disease severity. The same research group replicated these findings in a subsequent study [73]. Similar findings were also observed in patients with melanoma, where correlation analyses revealed that illness denial was significantly associated to higher levels of psychological distress [74]. In patients with plaque psoriasis, Jankowiak et al. [75] showed that denial, defined as a lower level of illness acceptance, was significantly associated with impaired quality of life.

Several studies have been performed to evaluate attitudes of denial in patients with diabetes [76‒82]. In particular, Hyphantis et al. [77] showed that illness denial was a significant predictor of poor adherence (defined as delayed engagement to treatment) in outpatients with type 2 diabetes. In evaluating patients’ attitudes toward insulin therapy in adults with type 2 diabetes, Rajab et al. [79] found similar results.

In patients with a diagnosis of type 1 diabetes mellitus, high levels of illness denial were found in 22% of the sample [83]. Karlsen and Bru [84] showed that 13% of their sample of patients with both types of diabetes responded to diabetes-related problems by illness denial. In a study with diabetes patients, of which 1,261 with type 2 diabetes, illness denial was detected in 7% of the sample [85]. Rajab et al. [79] reported the tendency to deny the severity of disease in 67.5% of patients with type 2 diabetes. A high prevalence of illness denial (33.8%) was also detected in a recent study involving patients with type 2 diabetes mellitus [86]. In a study investigating reasons for failure to achieve disease control in a group of 120 patients with long-standing acromegaly, illness denial was detected in 23.3% of the sample [87].

Several studies have been conducted to assess the extent to which illness denial affected clinical outcomes and recovery in patients with various forms of diabetes [85, 88‒92]. Peyrot and McMurry [90] showed a statistically significant relationship between illness denial and poor glucose control in a small sample of insulin-treated diabetic adults. Mühlhauser et al. [89] found that illness denial was a significant risk factor of severe hypoglycemia in a large sample of patients with type I (insulin-dependent) diabetes. Garay-Sevilla et al. [88] reported similar findings in a cross-sectional study involving patients with type 2 diabetes mellitus. They found that illness denial was a significant predictor of poor metabolic (i.e., glycemic) control [88].

Kiernan and Powers [93] were among the first to detect inappropriate reactions of illness denial in hepatitis B patients. They showed that 30% of patients denied the possibility of disease transmission [93]. The same authors reported similar prevalence rates in a subsequent study [94]. In a more recent study, illness denial was detected in 13.7% of patients with hepatitis B [95]. Using the DCPR, illness denial was found in 7 of the 190 patients (3.7%) with functional gastrointestinal disorders [96].

In a research study investigating the role of biological (e.g., immune parameters such as interferon-a and soluble interleukin-2) and psychological factors in determining disease progression, Rose et al. [97] concluded that illness denial may have a negative impact on recovery processes of patients with hepatitis A.

Several studies have been performed to assess the clinical role of illness denial in human immunodeficiency virus (HIV) patients [98‒103]. In a case-control study comparing patients with HIV and HIV-negative controls, Perkins et al. [102] found that in HIV patients, those with a personality disorder showed significantly greater use of illness denial and helplessness as mental and behavioral strategies to cope with the threat of acquired immune deficiency syndrome (AIDS). Commerford et al. [98] reported similar findings in a subsequent study with female patients with HIV/AIDS infection. Illness denial and problem-focused threat minimization were found to be associated with measures of anxiety and depression, meaning that the greater the use of these coping strategies, the higher was anxiety or depression [98]. In patients with HIV, illness denial was found to be associated with poor quality of life and with perceived stress [100, 103]. The use of illness denial as a form of coping was found to be associated with lower levels of physical and mental health-related quality of life [100]. Kiyingi et al. [101] showed that the initial denial of HIV infection was a significant predictor of delayed initiation of the therapy.

Prevalence rates of illness denial in HIV greatly varied across studies, from 9% of cases [104] to 74% [105], with intermediate results such as in 33% [106] and 28% of the samples [107]. In a prospective study of HIV patients who were enrolled in a tuberculosis preventive therapy program, illness denial (defined as the denial of the HIV infection status) was found in 11 of the 72 (15.3%) patients who demonstrated poor treatment adherence [108].

In a 2-year longitudinal study involving patients with AIDS, Ironson et al. [109] found that illness denial and poor adherence to behavioral interventions were significant predictors of disease progression, meaning that the higher the increase of illness denial and the lower the treatment adherence, the greater the likelihood of having symptoms at 2-year follow-up. Illness denial was also found to be significantly associated with a decline in the number of CD4 cells, which are immune markers of disease progression in the spectrum of HIV-related disorders [109]. In a subsequent prospective study involving patients with HIV type 1 infection without AIDS or symptoms at baseline, Leserman et al. [110] reported similar results and demonstrated that those who cope with the threat of AIDS by using illness denial have faster disease progression when followed for up to 7.5 years. Patients who used illness denial as a strategy of coping with HIV/AIDS were significantly more likely to report greater pain severity [111]. More recent studies were also conducted to evaluate the clinical role of illness denial in other infectious diseases [112, 113]. In a cross-sectional survey examining levels of perceived stress and coping mechanisms related to COVID-19, illness denial was found to be positively associated with optimal levels of psychological well-being [113]. In another cross-sectional investigation, illness denial was found to be significantly associated with an increase in levels of COVID-19-related stress [112].

Several studies evaluated the clinical role of illness denial in patients with various forms of renal disease [114‒117]. Short and Wilson [116] were among the first to show that illness denial may serve as an effective mental mechanism helping patients with chronic renal failure to cope with a continuing unsatisfactory situation. In a retrospective study, Richmond et al. [118] demonstrated that higher levels of illness denial were positively correlated with increased probability of success on home hemodialysis. In a subsequent cross-sectional investigation involving hemodialysis patients, Jadoulle et al. [119] reported similar findings. They found that illness denial was an efficient coping style having a protective effect against negative emotions, particularly against anxiety and depression [119]. The authors, however, showed that illness denial can reduce treatment compliance [119]. In a retrospective study of patients with chronic kidney disease, Obialo et al. [120] found that illness denial was a significant determinant of late and ultra-late referral and presentation for renal replacement therapy.

Jungers et al. [121] found that 40% of their late referral patients failed not only to acknowledge the existence of their chronic kidney disease but also to appear for follow-up visits with their nephrologist. Obialo et al. [120] reported similar results showing that illness denial, which was detected in 45% of their retrospective sample of patients with chronic kidney disease, was the predominant reason for delayed referral for renal replacement therapy. In a subsequent study involving patients with chronic kidney disease, illness denial was detected in 35.24% of the sample [122]. In kidney transplant recipients, DCPR illness denial was detected in 13.4% of the sample [123], with a high prevalence compared to other medical disorders (Table 2). In a cross-sectional investigation involving hemodialysis patients, Shamasneh et al. [124] found that 17.8% of patients denied their disease or even their need for hemodialysis. Alfarhan et al. [125] conducted a similar study reporting higher prevalence rates of denial of chronic kidney disease and of the need of hemodialysis that were detected in 76.4% of the sample.

In a research study involving chronic hemodialysis outpatients, Yanagida et al. [117] demonstrated that the higher was the level of denial, the lower were feelings of depression and a sense of helpless dependence. Similarly, in a study with end-stage renal disease patients, Fricchione et al. [126] showed that those with low levels of illness denial were more sensitive, had more anxiety and depression, and also reported greater sleep disturbances than patients with high levels of illness denial. In a more recent study involving pre-dialysis patients with chronic kidney disease, Pugi et al. [127] found that illness denial was a significant predictor of higher levels of health-related quality of life. The authors showed that chronic kidney disease patients with illness denial were not bothered by the effects of the kidney disease on daily life, did not perceive high levels of frustration and interference of kidney disease in their life, did not report any concentration problems or mental confusion [127]. In a cross-sectional investigation involving hemodialysis patients, however, Carvalho et al. [128] showed that illness denial was associated with impaired health-related quality of life. In a study of patients with peritoneal dialysis, the intensity of illness denial correlated with end-stage renal disease-related anxiety [129].

Many studies have been conducted to assess whether illness denial was a determinant of health attitudes and behavior in patients with cancer [1, 28, 130‒139, 141‒148][1, 28, 130‒139, 141‒148]. In particular, Lynch and Krush [138] showed that factors contributing to delay (defined as an interval of 3 months or longer between the time an individual first notices signs or symptoms of cancer and the time he/she seeks medical attention) in a heterogeneous sample of patients with various forms of cancer included attitudes of denial. In a more recent study, Panzarella et al. [149] found that illness denial was a significant predictor of diagnostic delay in patients with oral squamous cell carcinoma. Similarly, in a cohort study of newly diagnosed patients with lung cancer, Kotecha et al. [150] found that illness denial was one of the most significant patient-related causes of delay (defined as the time from first symptoms of lung cancer to contacting primary care). Contrasting results were also reported. For instance, Watson et al. [151] did not observe a statistically significant relationship between illness denial and increased delay in seeking medical treatment in a newly diagnosed group of patients with breast cancer.

Aitken-Swan and Easson [11] detected the initial reaction of illness denial to the diagnosis of cancer in 19% of the sample. In assessing why patients with various forms of cancer (e.g., breast, cervix, and lung cancer) delayed seeking medical advice, Henderson [152] found that the most common reason was denying the seriousness of symptoms (39.4% of the sample). Lebovits et al. [153] found similar prevalence rates. In a study conducted in patients with a diagnosis of lung cancer, denial was detected in 15% of the sample [154]. Evaluating cancer patients with the use of DCPR [21], Grassi et al. [155] documented illness denial in 8.2% of the sample. Vos et al. [156] investigated the prevalence of illness denial over time in newly diagnosed lung cancer patients. They found that most patients displayed a low (65%) or moderate (21.5%) level of illness denial at baseline, while only a small number (3%) showed a high level of illness denial [156]. They also found that the majority of patients continued to exhibit a low level of illness denial at subsequent assessments [156]. In evaluating the reasons for delayed diagnosis and treatment in a cohort of consecutive patients with non-melanoma skin cancer, Alam et al. [130] found that patients waited to see their doctor because of their illness denial. Specifically, the authors showed that the two most commonly reported reasons why patients delayed seeking medical care were thought it would go away (36% of patients) and thought it was not important (24% of the sample) [130]. Beesley et al. [157] detected illness denial in 74% of patients with ovarian cancer.

Several studies have been performed to evaluate the impact of illness denial on clinical outcomes and recovery in patients with various forms of cancer [151, 158‒173]. Greer et al. [161] conducted a prospective study involving consecutive patients with early breast cancer to examine whether particular coping responses affected long-term prognosis. They showed that recurrence-free survival at 5-year follow-up was significantly more common among patients who had initially reacted to cancer by denial than among those who had responded with stoic acceptance or with feelings of helplessness and hopelessness [161]. In a subsequent study using the same design and sample, Pettingale et al. [173] found that patients with psychological responses of denial to the diagnosis of cancer had significantly higher levels of serum immunoglobulins IgM than either those who responded with fighting spirit or stoic acceptance. Findings demonstrating the protective effect of illness denial were replicated in other longitudinal studies with follow-up evaluations of 10–15 years, where it was found that breast cancer patients who responded with illness denial were significantly more likely to be alive and free of recurrence than those with fatalistic or helpless responses [162, 174]. Watson et al. [151] reported that breast cancer patients who denied the seriousness of their diagnosis experienced significantly less mood disturbances and less anxiety than those who accepted the implications of their diagnosis, thus suggesting that denial rather than a confrontation-coping-response may effectively reduce psychological distress, particularly during the initial phase of hospitalization. Dean and Surtees [159] revealed that breast cancer patients employing a coping strategy of illness denial had a better chance of remaining recurrence-free during the follow-up period than those adopting other coping strategies. They also found that there was a statistically significant tendency for breast cancer patients with illness denial, at 3 months postoperatively, to have more chances of survival than those exhibiting other coping strategies [159]. Lehto et al. [175] reported similar findings showing that illness denial was a significant predictor of longer survival in patients with localized melanoma. They also found that illness denial was the only protective factor that predicted survival independent from other psychological variables [175]. Vos et al. [176] investigated the relationship between illness denial and clinical outcomes in a longitudinal investigation with newly diagnosed lung cancer patients: those displaying moderate or increasing denial reported better physical functioning, less nausea and vomiting, less appetite loss, and less dyspnea. They also found that moderate deniers suffered less from fatigue than low deniers and increasing deniers reported less fatigue over time [176]. In a subsequent study of newly diagnosed lung cancer patients, the authors prospectively investigated the relationship between illness denial and psychological outcomes [177]. They not only found that moderate deniers reported better emotional functioning, less anxiety, and less depression than low deniers but also showed that overall quality of life was significantly better among lung cancer patients who displayed either moderate or increasing levels of denial [177].

In a case-control study involving primary care patients who were assessed using the DCPR, illness denial was a common psychosomatic syndrome, which was detected in 68% of frequent attenders [178]. In a trial using the DCPR to assess psychosocial problems in primary care patients, illness denial was found to occur in 3.5% of the sample [179].

In evaluating psychological reactions of patients following a life-threatening attack of asthma, Yellowlees and Ruffin [180] observed that patients responded to this adverse event by either decompensating psychiatrically and developing symptoms of anxiety or by increasing their levels of illness denial. In a subsequent study with consecutive patients who presented to the emergency hospital with a near fatal attack of asthma, Campbell et al. [181] found that those with higher levels of illness denial were less likely to describe the presentation of asthma attacks as a progressive respiratory distress and more likely to report the presentation of these symptomatic episodes as a sudden respiratory collapse. The authors thus concluded that high levels of illness denial may be life-threatening since they may be an obstacle to the adoption of appropriate self-management strategies to control asthma and reduce the severity of attacks [181]. In patients with a diagnosis of asthma, illness denial and the level of adherence to asthma medication were not significantly correlated [182, 183].

In a study with consecutive cases of near fatal asthma attacks, illness denial was detected in 57% of patients [181]. In a subsequent study with near fatal asthma, illness denial was detected in 42% of the sample [184]. Gamble et al. [185] found that 160 of 182 patients (88%) with difficult asthma admitted poor adherence with inhaled therapy after initial denial. In a comparative study involving patients with end-stage chronic obstructive pulmonary disease, 26% of them appeared to be in denial [186].

In a prospective, randomized controlled trial of patients with moderate-to-severe asthma who did not have evidence of poor perception of bronchoconstriction on histamine challenge testing, Adams et al. [187] showed that those who had emergency hospitalizations were more likely to have higher baseline levels of illness denial, and more anxiety on both trait-anxiety and state-anxiety scales. In patients with a diagnosis of asthma, illness denial was a significant predictor of poor outcomes [188, 189]. In a cross-sectional study of patients with chronic obstructive pulmonary disease, higher levels of illness denial were found to be associated with impaired health-related quality of life [190].

In a comparative study examining differences in reactions to disability between a group of patients with early rheumatoid arthritis and a sample of patients with advanced rheumatoid arthritis, Treharne et al. [191] showed that illness denial may be an adaptive strategy to cope with disability, particularly in the early stages of this rheumatological condition.

Illness denial was found in 44.5% of subjects with rheumatoid arthritis [192]. Tesio et al. [193] conducted a comparative study investigating the prevalence rates of DCPR syndromes in patients with fibromyalgia compared with a group of rheumatoid arthritis patients. Illness denial was detected in 32.7% of patients with fibromyalgia and in 20.4% of those with rheumatoid arthritis [193].

In an exploratory cross-sectional study of spinal cord injury patients, Livneh and Martz [194] found that those with recent-onset spinal cord injury had higher levels of illness denial. In a subsequent study, emotional attitudes of denial were related to lower levels of adaptation to disability [195, 196]. Kortte et al. [197] found that greater rehabilitation engagement in patients with spinal cord injury was significantly related to lower levels of illness denial.

In a study with spinal cord injury patients, Cook [198] found that 34% of the sample had illness denial. In a subsequent study of patients with spinal cord injury, Fukunishi et al. [199] reported prevalence rates of illness denial (defined as disappearance of consciousness of disability) ranging from 13% to 31%.

In patients with a traumatic spinal cord injury, those with illness denial were more likely not only to be less depressed but also to reject the sick role [200]. Similar findings were reported in a subsequent longitudinal investigation involving patients with traumatically acquired spinal cord injury [201]. Opposite results were also observed [202, 203]. In a cross-sectional analysis of patients with traumatic spinal cord injury, the denial of illness was found to be significantly correlated with anxiety, depression, and hopelessness [202]. In another study, higher levels of illness denial were associated with lower levels of affective well-being [203]. In patients with paraplegia due to traumatic long-term spinal cord injury, illness denial was found to be negatively correlated to measures of posttraumatic growth [204]. In subsequent studies with spinal cord injury patients, illness denial was a significant predictor of higher levels of symptoms of anxiety [205] and was also found to be negatively associated with basic hope and a general sense of self-efficacy [206].

The findings of this systematic review indicate that illness denial is a significant determinant of health attitudes and outcomes in different medical disorders. Its prevalence (ranging from 1.8% to 74%) may vary as a function of the measure used, the specific disorder, and the medical setting. Illness denial appeared to play a major clinical role in the process of convalescence, in the self-management of chronic conditions such as diabetes, and in determining disease progression and a state of recovery, as well as the likelihood of early recognition of life-threatening diseases (e.g., cancer, myocardial infarction, near fatal attacks of asthma) and their prompt treatment. Despite its high prevalence and its influence on the course, therapeutic response, and clinical outcome of several medical disorders, illness denial is not included in the customary taxonomy, particularly in diagnostic classification systems such as the Diagnostic and Statistical Manual of Mental Disorders (DSM) [207] or the International Classification of Diseases (ICD) [208].

The findings of this review also indicate that as a general mechanism denial is not necessarily dysfunctional but may serve important adaptive functions. It may help a person cope with various phases of illness and treatment by allowing time to process and dilute distressing information at a manageable rate, as was found to occur in cancer [209]. Patients who had low levels of denial did not delay in reporting their symptoms to the medical attention, did not require outside help to seek medical help, were more likely to exhibit health-promoting attitudes and behavior, and had more favorable clinical outcomes [27, 37, 53, 56, 57, 59, 118, 119, 126, 127, 161, 173, 175, 176]. Denying the burden of physical disease may indeed be an adaptive coping mechanism in some circumstances and at certain degrees, as in the early stages of the disease, for example, immediately after diagnosis, or in the terminal phase of a life-threatening disease because it may alleviate psychological distress, as well as symptoms of anxiety and depression [25, 37, 49, 52, 210]. Illness denial may also improve clinical outcomes [56, 59, 68, 127, 159, 161, 173, 175]. The following clinical findings exemplify these phenomena: (1) unstable angina pectoris patients with illness denial were more likely to reach medical stabilization [56], (2) illness denial was a significant predictor of good recovery in cardiac patients with myocardial infarction [59], (3) chronic pain patients with illness denial reported lower levels of disability [68], (4) in patients with chronic kidney disease illness denial predicted higher levels of health-related quality of life [127], (5) patients who had initially reacted to cancer by denial were significantly more likely to be alive and free of recurrence at a 5-year follow-up evaluation and had significantly higher levels of serum immunoglobulins IgM than either those who responded with fighting spirit or stoic acceptance [173], (6) illness denial was a significant predictor of longer survival in breast cancer patients and in those with localized melanoma [159, 161, 175]. In these clinical situations, where illness denial may not only provide protection against painful and distressing experiences but also facilitate coping with difficult situations and improve both short- and long-term outcomes, it can be viewed as an adaptive process [16]. However, high levels of denial may be dysfunctional and associated with delay in seeking treatment, impaired adherence, and treatment refusal [109, 110, 188, 189, 211]. For instance, Campbell et al. [181] demonstrated that illness denial was a significant barrier to the adoption of appropriate self-management strategies to control asthma and reduce the severity of attacks. Garay-Sevilla et al. [88] showed that in patients with type 2 diabetes mellitus illness denial was a significant predictor of poor metabolic (i.e., glycemic) control. In another study with post-myocardial infarction patients, illness denial was found to be associated with an increased risk of being non-adherent to medications [44]. Among patients with lung cancer, illness denial was one of the most significant causes of delay in seeking medical help [150]. In these cases, where illness denial inhibits actions of potential importance (e.g., refusal of medical attention or poor compliance with necessary treatment), it should be regarded as maladaptive [16, 19].

Criteria of gradation are thus needed to assess the degree of illness denial and its impact on clinical outcomes. The DCPR criteria [21, 22], with their semi-structured interview [212], may help clinicians and investigators to set a severity threshold for illness denial and other health attitudes and behavior. However, it is not just a matter of grading intensity. The criterion B of the DCPR (Table 1) requires the fact that the patient has been provided with an adequate appraisal of the medical situation and management (if any) to be followed, with opportunity for discussion and clarification [22]. Denial should not be confused with lack of adequate information and/or misunderstandings that may occur in the medical system, that may be amenable to improvement through provision of medical information and adequate explanation. This shared decision-making approach, which requires an empathetic and communicative physician-patient relationship, is particularly important in individuals with limited health literacy, who would otherwise be prone to worse self-management, lower use of preventive services, and higher hospitalization rates [211].

The findings of this systematic review disclose that illness denial was frequently associated with other health attitudes and behavior related to disease perception and treatment seeking. As a result, evaluation of illness denial needs to be placed within a unifying spectrum [211]. On one side of the spectrum, there are manifestations that are characterized by anxiety, with particular reference to worry about illness, concern about pain and bodily preoccupations. On the other side of the spectrum, there are various forms of health-damaging behavior that range from unrealistic optimism to delay in seeking medical care, from partial or total lack of adherence to complete denial of diagnosis and of the need for treatment [211]. As important is relating illness denial to affective disturbances that may influence its expression, such as anxiety, depression, demoralization, and irritable mood [22, 213].

The findings of this systematic review also highlight the lack of trials that are concerned with treatment or modification of illness denial. The effectiveness of specific management strategies or intervention procedures needs to be tested in randomized controlled trials and this area of research deserves high priority in funding.

The clinical evaluation of illness denial in medical settings is a major health care challenge that requires a unifying conceptual framework for the wide range of attitudes and behavior related to the complex balance between health and disease, adoption of a psychosomatic assessment of its multidimensional characteristics, and use of appropriate clinimetric methodology for its determination [22, 35, 214, 215]. Clinimetric indices such as the DCPR that make full use of the clinical experience and skills of the interviewer may address the psychological mechanisms of denial and the level of communication that has occurred between patient and physician, while self-rated scales have considerable limitations in covering such aspects.

An ethics statement is not applicable because this study is based exclusively on the published literature.

The authors have no conflicts of interest to declare.

There were no sources of funding for this work.

Chiara Patierno and Danilo Carrozzino searched, screened, and selected studies; both authors extracted data. Giovanni A. Fava supervised the study selection and data extraction. All the authors conceived the work and drafted and finalized this paper.

All data generated or analyzed during this study are included in this article and its online supplementary material files. Further inquiries can be directed to the corresponding author.