Microsporum canis infection mimics pemphigus erythematosus.

We report a 55-year-old Japanese woman with a two-month history of multiple pruritic erythema and erosion on her face and neck. Based on the clinical appearance, we initially diagnosed her as having pemphigus erythematosus. However, the results of a histopathological examination and a direct immunofluorescence study did not support the initial diagnosis. Additionally, anti-desmoglein 1 and 3 antibodies were all negative. Subsequently, a microscopic examination of scales revealed filaments of fungi and a fungal culture was negative for macroconidium. Using molecular biology techniques, we identified the fungus as Microsporum canis, which causes a zoonotic infection. The immune reaction to the fungi could be drastic and therefore, the eruption sometimes displays atypical clinical manifestations.

What was known?

1. Fungal infections are very common skin diseases that are easy to be diagnosed, mainly when the fungus can be identified microscopically. However, in case of zoonotic infection such as Microsporum canis, it is difficult to be diagnosed because of atypical clinical manifestations.

2. Additionally, misdiagnosis leads to inappropriate treatments which will modify the skin lesions. This in turn makes the accurate diagnosis rather difficult.

Introduction

Dermatophytes infections are still one of the most important groups of fungal infections worldwide.[1-3] Once the diagnosis of a dermatophyte infection is made, it is relatively easy to treat it. Identification of dermatophytes is usually based on the morphological characteristics of mature large colonies and microscopic examinations. When a definitive diagnosis cannot be made, molecular biology-based techniques such as polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP), are useful to identify the species of dermatophytes.[4-6] We herein report a 55-year-old patient with Microsporum canis infection of the face mimicking pemphigus erythematosus, and we confirmed that the causative fungus was Microsporum canis by using PCR-RFLP methods.

Case Report

A 55-year-old woman presented with a two-month history of skin rash in February 2011. Physical examination revealed multiple pruritic erythema and erosion on her face and neck with unremarkable mucosal lesions [Figure 1a]. Based on the clinical finding, we initially made the diagnosis of pemphigus erythematosus.

Figure 1

Clinical features (a) Physical examination revealed multiple pruritic erythema and erosion on her face and neck, (b) After treatment with an antifungal agent, the symptoms dramatically improved

Laboratory tests showed slightly elevated serum AST and ALT. Anti-desmoglein 1 and 3 antibodies, antinuclear antibodies, anti-SS-A and anti-SS-B antibodies were all negative. Histological examination revealed crust, acanthosis, mild spongiosis and scattered neutrophilic infiltrations in the epidermis, and perivascular mononuclear cell infiltrations in the upper dermis, however, neither vesicle nor bulla was seen. We then obtained the information that she had started keeping a cat at her house before the eruption appeared, and so we suspected that the infection could be fungal. Further mycotic examination revealed fungal filaments; however, the fungal culture on Sabouraud agar did not show macroconidium. Therefore, we investigated the species of fungi using a PCR-RFLP (polymerase chain reaction-restriction fragment length polymorphism) according to a previous report by Mochizuki, et al.[4] Briefly, we extracted DNA from cultured mycotic substances, and then the DNA samples were amplified. Finally, the PCR products were treated with restriction enzyme in the RFLP analysis, such as Mva I and Hinf I. As shown in [Figure 2], we confirmed that the fungus in her skin lesions was Microsporum canis. We treated her with a topical antifungal ointment, luliconazole (Lulicon Cream®). The treatment dramatically improved her eruption [Figure 1b].

Figure 2

The PCR products were treated with restriction enzyme in the RFLP analysis, such as Mva Iand Hinf I.M indicates marker DNAs. The numbers on the left side of each panel indicate the sizes of the molecular markers (bp)

Discussion

Clinically, a Microsporum canis infection appears as multiple round exudative lesions with scales and crusts, mostly along with the periphery of erythema.[7] Our patient had been treated with a corticosteroid ointment and/or a topical anti-fungal ointment at other clinics. The previous treatments modified her skin lesions, which made it more difficult to make an accurate diagnosis. Dermatophytes are divided into three genera, Trichophyton, Epidermophyton and Microsporum, and have the ability to invade keratinized tissues, such as the hair, skin and nails of humans as well as other animals. Microsporum canis infection is zoonotic and is mostly transferred by cats.[8] Zoonotic infections sometimes elicit strong immunological reactions in humans.[9] Additionally, misdiagnosis leads to inappropriate treatments, as in our case, and may cause atypical clinical presentations. Classification of dermatophytes is usually based on the morphological characteristics of mature large colonies and microscopic examinations of spores and hyphae on slide culture. Morphological identification often takes time because it is necessary to culture the fungi. Molecular biology-based techniques such as PCR and RFLP are being used to identify dermatophytes, providing a rapid and accurate diagnosis.[4-6]

In our case, the culture of fungi did not show macroconidium even though various culturing methods were used. PCR-RFLP proved to be a useful technique for an accurate identification of the causative fungus.

What is new?

A fungal infection, in a certain occasion, appears with atypical clinical manifestations such as pemphigus erythematosus. Though, culture of such fungi with various culturing methods, it does not show macroconidium. In this case, PCR-RFLP proved to be a useful technique for an accurate identification of the causative fungus.