Curvularia lunata-Induced Onychomycosis in an Unlikely Host: A Case Report

Onychomycosis is a fungal disease affecting the nail apparatus. It can present with various manifestations such as subungual hyperkeratosis, onycholysis, and nail plate destruction [1]. Established risk factors for onychomycosis include trauma, advanced age, and history of tinea pedis [2]. Additionally, comorbidities such as diabetes, obesity, immunosuppression, and malignancies are associated with an increased risk [2]. Onychomycosis can be caused by various fungi including dermatophytes, yeasts, and nondermatophyte molds NDM [3]. The prevalence of onychomycosis varies due to several influencing factors. Generally, dermatophyte infections, also referred to as tinea unguium, are the most common, representing 60–70%. In contrast, nondermatophyte molds contribute 30–40%, and yeast infections account for 10–20% [2]. Trichophyton rubrum is the predominant dermatophyte in onychomycosis, constituting approximately 45% of infections [2]. Other dermatophytes implicated include Trichophyton mentagrophytes, Epidermophyton floccosum, Microsporum species, and other Trichophyton species. While the yeasts most frequently isolated from onychomycosis are Candida species [3]. As for the molds, a variety of them have been isolated from nails [4]. According to Ramani et al. [4] study results, a 22% culture positivity rate for molds in onychomycosis cases was found. Notably, the predominant mold isolates comprised Aspergillus species (86.4%), Fusarium oxysporum (4.5%), Curvularia species (4.5%), and Penicillium species (4.5%).

The most prevalent presentation of fungal nail infection is distolateral subungual onychomycosis. Toenails are more commonly affected than fingernails are. The fungus invades the nail and the nail bed by penetrating the distal or lateral margins. The affected nail thickens and discolors, with different degrees of onycholysis. Invasion through the proximal margin, which is embedded within the proximal nail fold, is more prevalent in immunodeficient (proximal subungual onychomycosis) [1]. Progression of the disease can lead to variants and overlap of these presentations. Curvularia lunata is a saprobic dematiaceous mold that resides primarily in soil [4]. They spread via airborne spores and are a common cause of disease in plants. Curvularia can be microscopically distinguished from other dematiaceous fungi due to the presence of curved conidia [5]. The first reported human case was in 1959 as a corneal infection. Of approximately 40 recognized species, the most common causing human infection is C. lunata [5]. Reports of human disease caused by this organism are rare but include endocarditis, brain abscess, skin infections, onychomycosis, keratitis, pneumonia, disseminated disease, mycetoma, allergic bronchopulmonary disease, and one case of sinusitis [5]. This case is reported due to rarity of onychomycosis caused by Curvularia in immunocompetent individuals.

The patient is 53-year-old male engineer with a 1-year history of leukonychia in the distolateral aspect of his left big toenail (shown in Fig. 1). He mentioned a history of minor trauma but denied a history of diabetes mellitus, infectious, or autoimmune conditions. His BMI at presentation was 24.6, indicating a normal weight range. He was a nonsmoker and reported occasional alcohol consumption.

The patient’s medical history revealed dyslipidemia and coronary artery disease, for which he underwent stent placement 3 years prior to presentation. Ongoing management involved the regular administration of rosuvastatin, aspirin, and ticagrelor. Prior to the consultation, the patient had not received any topical or systemic treatments for the nail discoloration. During physical examination, whitish-yellow discoloration was observed on the distolateral portion of the left big toenail. The other toenails were normal.

In response to the clinical presentation, KOH preparation of nail scrapings was done and was positive for fungal elements. A nail culture was promptly ordered. The results of the culture confirmed the presence of C. lunata, indicating a fungal etiology for the observed toenail discoloration. Due to the opportunistic nature of the identified infection, a laboratory examination was conducted to assess for underlying immunosuppression, and the results returned negative.

The standard therapeutic approach for Curvularia onychomycosis usually involves either oral itraconazole or oral terbinafine hydrochloride [6]. Due to the identified interaction between oral itraconazole and ticagrelor (categorized as Risk Rating X with a recommendation to avoid concurrent use), the patient was instead prescribed a daily dose of 250 mg oral terbinafine for 6 months, to which he adhered. At the follow-up after 6 months, the patient showed a complete resolution of the discoloration on physical examination (shown in Fig. 2).

Various studies have shown that the incidence of onychomycosis due to NDM has recently increased [7]. Curvularia species are ubiquitous; they reside primarily in soil and occasionally lead to infections in humans. Notable distinctions in presentation and severity of Curvularia infections are evident when comparing immunocompromised and immunocompetent patients. Immunocompromised individuals exhibited a more pronounced susceptibility to Curvularia, often presenting with more aggressive and disseminated forms of the infection encompassing conditions such as sinusitis, keratitis, pneumonia, mycetoma, allergic bronchopulmonary disease, endocarditis, brain abscess, and disseminated disease [1]. In contrast, immunocompetent patients typically experience localized and less severe manifestations of Curvularia infections, often limited to conditions like onychomycosis [7]. Curvularia molds exhibit deep pigmentation owing to melanin in their hyphae and conidia, a characteristic that contributes to their pathogenicity [4]. The species causing human infections include C. lunata, Curvularia pallescens, and Curvularia geniculata. Transmission occurs through inhalation or inoculation often triggered by factors such as perspiration, trauma, and exposure to soil saprophytes [7]. Cutaneous infections attributed to Curvularia tend to favor the extremities, often following a traumatic inoculation. Notably, toenail trauma has the potential to cause disruptions in the nail structure, creating entry points for fungal pathogens, including Curvularia. Furthermore, environmental exposure to soil and plant material is a recognized risk factor, as these environments harbor Curvularia species, increasing the likelihood of inoculation [8]. This highlights the role of occupational or recreational exposure in predisposing individuals, even those who are immunocompetent, to Curvularia-induced onychomycosis. These factors provide a plausible explanation for the occurrence in our patient. Therefore, it is crucial to conduct a thorough history, including inquiries about occupation, recreational activities, or any routine linked to potential modes of transmission.

During the physical examination, patients often exhibit nail dystrophy suspicious of onychomycosis, such as discoloration, thickening, splitting, and nail plate destruction. Accurate identification of C. lunata in nail infections requires a combination of direct microscopy, culture, and, when available, molecular techniques. The pigmented nature of the fungus can be observed in direct microscopy, but its similarity to other dematiaceous fungi necessitates culture for definitive identification. Molecular methods, though not always accessible, can provide precise species-level identification, which is crucial for appropriate management [1, 2, 9]. The scarcity of properly conducted paraclinical examinations, such as fungal cultures for onychomycosis cases, may partially explain the infrequent detection of specific organisms. When diagnostic methods, such as cultures, are not routinely performed or are inadequately implemented, certain fungal organisms may go unnoticed. This lack of comprehensive testing can lead to underreporting and contribute to the perceived rarity of onychomycosis caused by certain fungal species, including Curvularia. In essence, the rarity might be attributed, at least in part, to the limitations in diagnostic practices, highlighting the importance of utilizing comprehensive paraclinical exams for a more accurate understanding of the prevalence and causative agents in onychomycosis cases.

Precise identification of the causative organism in onychomycosis is crucial for guiding appropriate antifungal therapy, particularly considering the growing concern of antifungal resistance. Current treatment options for dematiaceous fungi infections like Curvularia-induced onychomycosis include azoles (such as voriconazole, itraconazole), amphotericin B, terbinafine, and echinocandins [6]. Nevertheless, determining the most effective antifungal therapy remains uncertain. Consequently, physicians would carefully weigh factors such as infection severity, overall health, potential medication side effects, and drug-drug interactions to formulate a tailored management plan for each patient based on his personal factors.

Oral antifungal medications, such as terbinafine and itraconazole, are considered the first-line treatment for onychomycosis due to their superior efficacy. These are typically preferred except in cases of mild onychomycosis or patients with polypharmacy. In such situations, topical antifungals like terbinafine or ciclopirox may be recommended. However, the effectiveness of topical treatment can be limited by challenges such as restricted access to the nail bed and the pharmacologic properties required for adequate nail plate penetration [6]. Oral antifungals, while effective, require careful monitoring due to potential risks. Terbinafine has been associated with hepatic injury, necessitating liver function tests during treatment. Itraconazole, on the other hand, carries a high risk of drug interactions and should be used cautiously in patients with cardiac conditions. Fluconazole, another oral antifungal, may prolong the QT interval and poses cardiovascular risks [6].

Regarding nail debridement, which includes the trimming and removal of the infected nail portion, it can improve the efficacy of topical treatments. It is imperative to adhere diligently to the prescribed treatment regimen, as the management of onychomycosis often demands patience and consistency. Furthermore, preventing reinfection through the practice of good foot hygiene, maintaining dry feet, and avoiding environments conducive to fungal growth is crucial [10]. The prognosis for C. lunata onychomycosis in immunocompetent patients is generally favorable with appropriate antifungal therapy. However, recurrence can occur, underscoring the importance of regular follow-up to monitor treatment response and ensure complete resolution of the infection [9].

In conclusion, this case report underscores the rarity of onychomycosis caused by Curvularia in immunocompetent individuals, shedding light on the importance of considering less common fungal etiologies in clinical practice. The patient, a 53-year-old male with a history of toenail trauma and underlying cardiovascular conditions, presented with whitish-yellow discoloration in the distolateral aspect of his left big toenail. Through a comprehensive diagnostic approach, including KOH preparation, and fungal culture, C. lunata was identified as the causative agent. The patient’s treatment posed a challenge due to drug interactions with ticagrelor, necessitating an alternative therapeutic strategy with oral terbinafine, resulting in successful resolution of the lesion. The discussion highlights the increasing incidence of onychomycosis caused by nondermatophyte molds and emphasizes the need for accurate identification of causative agents through comprehensive paraclinical examinations. The limitations in diagnostic practices may contribute to the perceived rarity of certain fungal species causing onychomycosis. Treatment considerations involve weighing factors such as infection severity, overall health, and potential drug interactions, with oral antifungals, topical treatments, and nail debridement being viable options. Patient education on foot hygiene and regular follow-ups are crucial components of a successful management plan. This case report provides valuable insights for clinicians managing onychomycosis cases, especially those involving less common fungal pathogens. 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/10.1159/000543525).

This study protocol was reviewed and the need for approval was waived by The Lebanese American University (LAU) Institutional Review Board (IRB). Written informed consent was obtained from the patient for publication of the details of their medical case and any accompanying images.

None declared.

This study was not supported by any sponsor or funder.

Grace Obeid was involved in the direct care of the patient and collecting the information and data needed. Marwa Hallal wrote the manuscript and revised its intellectual content. All authors reviewed and approved the final version of the manuscript.

All data underlying the results are available as part of the article and no additional source data are required. Further inquiries can be directed to the corresponding author.