Addressing Diagnostic and Therapeutic Challenges in a Case of Concurrent Tinea and Plaque Psoriasis

Dermatophytes, with an affinity for keratin, are responsible for the majority of superficial fungal infections in humans. They are known to occur commonly among immunocompromised hosts [1].

However, these cases are underreported among individuals with immune-mediated inflammatory conditions, particularly chronic plaque psoriasis [2, 3]. Methotrexate (MTX), a metabolic antineoplastic medication, has demonstrated efficacy and cost-effectiveness in treating all forms of psoriasis [4]. Despite the advent of biologics, it remains a widely recommended treatment for individuals with psoriasis and psoriatic arthritis [5]. In addition, opportunistic fungal infections have been linked to prolonged administration of MTX as a consequence of immunosuppression [6, 7]. In this report, we present a case of worsening and undiagnosed tinea corporis in a patient with long-lasting plaque psoriasis after receiving MTX treatment.

A 45-year-old man with biopsy confirmed psoriasis and a Psoriatic Area and Severity Index (PASI) of 12.9 was being treated with tablet MTX (7.5 mg, once a week) and topical corticosteroids for a year. While certain lesions improved, new annular truncal and inguinal lesions emerged (shown in Fig. 1), which were treated by applying topical steroids and increasing the MTX dosage to 12.5 mg. Nevertheless, whenever the patient reduced the use of topical steroids, the annular lesions reappeared with increased severity. Exasperated by the inability of the local doctors and chemists to resolve the recurrent and fluctuating nature of the disease, he eventually sought treatment at our tertiary care medical facility.

Cutaneous examination revealed widespread erythematous plaques with greyish-white scales over the neck, abdomen, groin folds, buttocks, and back. Dermoscopy of these lesions showed minimal scaling with a rim of erythema (shown in Fig. 2). Potassium hydroxide analysis of skin scrapings from the lower abdomen revealed spiral hyphae with clustered microconidia, confirming trichophyton mentagrophyte as the etiologic agent. Histopathological examination demonstrated fungal hyphae within the epidermis (shown in Fig. 3). Based on the dermoscopic, mycological and histological findings, a diagnosis of tinea incognito complicating long-standing plaque psoriasis was made.

The administration of tablet MTX and topical steroids was discontinued, and oral itraconazole 200 mg (taken once daily) was initiated along with the application of luliconazole cream, for a duration of 2 months to eliminate the skin infection. After a month of therapy, the PASI subsequently increased to 16.8 and thus narrowband ultraviolet B therapy was given to control this psoriasis flare. A repeat potassium hydroxide mount after 2 months showed no evidence of fungal hyphae and thus tablet MTX (7.5 mg, once weekly) was restarted. The patient was educated about the application of steroids only on psoriatic plaques and topical antifungal creams on the remnants of tinea corporis.

The coexistence of tinea corporis with psoriasis is considered a rare occurrence, as the rapid turnover of psoriatic skin decreases the ability of fungi to invade the stratum corneum [3]. Nevertheless, this hypothesis is likely to be false. Arieli et al. [8] conducted an experimental study where they deliberately introduced dermatophytes onto psoriatic lesions and discovered that T. rubrum infected psoriatic skin at a significantly higher rate compared to the healthy skin of the same individuals. Furthermore, Noah discovered the presence of dermatophytes on the skin of individuals with psoriasis and identified them as potential contributors to the worsening of psoriasis symptoms [9]. In addition, the administration of biologics, immunosuppressives, or topical steroids can decrease the body’s immune responses, making the skin more vulnerable to dermatophyte infections [3, 10].

The differentiation between psoriasis plaques and tinea, which have similar morphology, can be ambiguous, resulting in an incorrect diagnosis [11]. A severe or widespread infection could result from an erroneous or delayed diagnosis when immunosuppression is present. The resemblance between the two conditions and the temporary relief of tinea symptoms by topical steroids caused a delay in the diagnosis and significant frustration in our patient.

In the absence of a response to immunosuppressant therapy or the emergence of new plaques, alternative diagnoses, such as fungal infections, should be considered. Clinicians must employ mycological or histological tests to rule out dermatophyte infections whenever such a suspicion arises. In addition, it is imperative that healthcare professionals conduct routine monitoring of patients who are prescribed long-term immunosuppressive therapy to proactively mitigate the risk of further complications or illnesses. The CARE Checklist has been completed by the authors for this case report, attached as online supplementary material (for all online suppl. material, see https://doi.org/10.1159/000542483).

The authors have no ethical conflicts to disclose. The research was conducted ethically in accordance with the World Medical Association Declaration of Helsinki. Written informed consent was obtained from the patient for publication of the details of their medical case and any accompanying images. Ethical approval is not required for this study in accordance with local or national guidelines.

The authors have no conflicts of interest to declare.

No sources of funding were used to assist in preparation of this manuscript.

All authors made equal efforts in structuring this case report. Conception and design of the study and revising the manuscript for critically for important intellectual content: Aayush Gupta. Data collection and patient care: Divya Asnani. Introduction, discussion and drafting the manuscript: Shrishti Singh and Divya Asnani. All authors approved the version of the manuscript to be published.

All data that support the findings of this study are included in this article and its online supplementary material. Further inquiries can be directed to the corresponding author.