INTRODUCTION

Steroid is one of the most commonly prescribed medication for various dermatologic diseases, providing effect through various pharmacologic activity like immunosuppression and anti-inflammation. However, even with proper usage, long-term use of steroid can cause iatrogenic dermatologic diseases. Tinea incognito is a steroid-induced skin condition of a superficial mycosis, characterized by loss of its typical feature such as elevated margin or scale due to decreased inflammatory response[1]. Many case reports and study concludes these atypical feature most often resemble eczema (82%), and others resemble psoriasis, lupus erythematous, or impetigo[2]. Herein, we present a case of a 27-year-­old patient with tinea incognito of trunk and upper arms, who was first misdiagnosed as aggravated atopic dermatitis with folliculitis, with review of literatures.

CASE

The patient is a 27-year-old male, who had visited dermatologic clinic with complaint of pruritic erythematous macules and nodules, first manifested a month ago. Previous treatment included systemic and topical steroid and systemic roxithromycin for six weeks under the impression of aggravation of atopic dermatitis and secondary bacterial infection, but the symptom had not improved.

Since childhood he had been taking both oral and topical steroid and antihistamine for atopic dermatitis; he had a history of truncal folliculitis which was treated with oral doxycycline. There was no specific family or social history, nor a history of animal contact.

Erythematous macules and papules, scattered widely on the upper trunk involving front chest and back area was noticed, and the same lesions were also found on both shoulders and upper arms (Fig. 1A). In addition, thick and easily broken yellow toenails with onset of two years ago were noticed (Fig. 1B). Lab findings were within normal range. KOH exam was done on one of the papules and first toenail, and hyphae were observed in both specimens (Fig. 2A). Scales from the lesions were cultured for three weeks on Sabouraud's dextrose agar plate, revealing elevated white cotton-like hyphae with dark reddish colony on the back side of the plate (Fig. 2B, 2C). Slide specimen was made from this colony and dyed with lactophenol cotton blue, which showed many teardrop-like microcon- idia under the microscope; the pathogen was identified as Trichophyton rubrum (Fig. 2D).

With confirmed diagnosis of tinea incognito by Trichophyton rubrum and concomitant onycho- mycosis, 12 weeks course of oral itraconazole 200 mg/day and 1% Flutrimazole ointment was started. The patient has recovered over time and the skin lesion improved with partial pigmentation (Fig. 3A, 3B).

DISCUSSION

Treatment must be preceded by accurate diagnosis, and visual inspection is one of the most important tools of diagnosis. This is especially true in dermatologic diseases, where a number of diseases can be diagnosed with visual inspection alone. However, atypical presentation may delay diagnosis and mislead the doctors; tinea incognito is one of such examples.

Tinea incognito is defined as superficial fungal infection with loss of typical presentation due to prior use of steroid medication, and was first reported by Ive and Marks in 1968[3]. As topical steroids and immunosuppressants like calcineurin inhibitors are being more and more used in many skin diseases like atopic dermatitis, psoriasis, contact dermatitis, or seborrheic dermatitis, tinea incognito has become more common and more studies are being published[2]. Its atypical presentation is thought to be caused by suppression of inflammation against fungi by immunosuppressants[4]. This allows fungi to slowly proliferate with relatively less erythema and scale, resulting in the lack of typical features.

Various fungi are responsible for tinea incognito, and Trichophyton rubrum consists about 70% of total pathogen in Korea, followed by Trichophyton mentagrophytes and Microsporum canis. This is in accordance with the study published in Italy, while the study in Iran reported Trichophyton verrucosum to be most common, and Trichophyton rubrum accounts for about 12% of the cases[5][6]. The reason Trichophyton rubrum is the most common pathogen is that it is one of anthropophilic dermatophyte, and is also the most common pathogen of human superficial fungal infection. In Iran, the most common fungus causing superficial infection is reported to be Epidermophyton floccosum, and Trichophyton verrucosum is the third most common pathogen[7]. Tinea incognito in Iran occurs mostly in rural area where contact with livestocks are common, and the superficial infection in the case of frequent contact with livestocks is most often caused by Trichophyton verrucosum, explaining how the same pathogen is responsible for tinea incognito in the most cases[8].

The patient in this case had had treatment for atopic dermatitis, and had onychomycosis since two years ago. Patients with atopic dermatitis are more prone to fungal infection, and onychomycosis may cause autoinoculation of the pathogen[9][10]. One study suggests the risk factors of tinea incognito are 1) Persistent erythematous, scaly skin lesion, 2) Lesions unresponsive to steroid or calcineurine inhibitors, 3) Lesions on truncal or facial area, 4) Concomittant fungal infection such as tinea pedis, onychomycosis, etc., 5) patients with suppressed immunity or taking immunosuppressants. If these risk factors are present, one must suspect tinea despite inconsistent features, and confirm the diagnosis with KOH exam and fungal culture[2].

Tinea incognito has shown various manifestations, but folliculitis-like features have been rarely reported. Akram A et al.[6] have argued topical steroids against skin infection might cause deeper fungal invasion into follicles.

Our case was the case of tinea incognito, misdiagnosed as folliculitis with atopic dermatitis aggravation because of previous history of folliculitis a year ago and signs of erythematous nodules, macules and patch. These lesions can spread to trunk and upper extremities and exacerbate atopic dermatitis, so accurate diagnosis by KOH exam and fungal culture, and antifungal treatment is necessary. Pityrosporum folliculitis can be considered as a differential diagnosis. However, the presence of macular patch lesions and surrounding papular lesions is thought to have spread from dermatophyte infection. In addition, folliculitis lesions were confirmed by Trichophyton rubrum through myco- logical examination. Therefore, it was diagnosed to be tinea incognito by Trichophyton rubrum rather than pityrosporum folliculitis

We authors report a case of tinea incognito with features mimicking folliculitis, in the patient with atopic dermatitis and onychomycosis, believing it will help future dermatologic practice.

Conflict of interest

In relation to this article, I declare that there is no conflict of interest.