Targetoid bullous tinea corporis: Unusual presentation of a dermatophyte infection

Sir,

Bullous lesions in tinea are uncommon and are usually seen in the setting of tinea pedis. Commonly reported causative fungal pathogens are Trichophyton rubrum and Trichophyton mentagrophytes.¹ We report a case of Microsporum canis causing targetoid bullous tinea corporis.

A 35-year-old woman gave a 6-day history of a generalised pruritic eruption involving the trunk and limbs. She had travelled to Kuantan, Malaysia and Bintan Island, Indonesia, in the past few weeks. One week prior to the onset of the rash, whilst in Kuantan, she had carried a stray kitten which scratched her on the neck. She reported no other contactants or medications prior to the eruption. She had no fever or mucosal involvement and was otherwise systemically well. Her past medical history was significant only for female pattern hair loss and alopecia areata, which was quiescent. On examination, multiple umbilicated targetoid papulovesicular lesions were seen over the neck, trunk, upper and lower limbs [Figure 1a-c]. The palms, soles, oral and conjunctival mucosae were not involved. She did not have any lymphadenopathy.

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Figure 1a:

Multiple umbilicated targetoid papulovesicular lesions over the neck and trunk

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Figure 1b:

Multiple umbilicated targetoid papulovesicular lesions over the neck, trunk, and upper limbs

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Figure 1c:

Close-up view of targetoid papulovesicular lesions over the right forearm

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The differential diagnoses considered were erythema multiforme, syphilis, ecthyma, orf and cat scratch disease. A full blood count was unremarkable and rapid plasma reagin was negative.

Histology from the edge of a left forearm blister showed subcorneal neutrophils, spongiosis of the epidermis with neutrophilic exocytosis and prominent upper dermal oedema resulting in subepidermal pseudovesiculation, as well as septate fungal hyphae within the stratum corneum, which were seen on periodic acid–Schiff and Gomori methenamine silver stain [Figures 2a and b].

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Figure 2a:

Epidermal spongiosis with subcorneal neutrophils, and prominent upper dermal edema resulting in subepidermal pseudovesiculation (H and E, ×40)

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Figure 2b:

Septate fungal hyphae within the stratum corneum (Periodic acid-Schiff stain, ×200)

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She was diagnosed with bullous tinea corporis and commenced on oral terbinafine 250mg daily. Her lesions completely cleared in 3 weeks [Figures 3a and b]. Cultures from the biopsy later returned positive for M. canis.M. canis is a zoophilic fungus, which usually causes infection in dogs, cats, and other animals.² The first case of M. canis causing bullous tinea was reported in 1993 and we found only 3 reports in the published literature.³ Our patient had a clear history of contact with a likely infected animal.

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Figure 3a:

Complete resolution of the patient’s lesions after 3 weeks of oral terbinafine

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Figure 3b:

Complete resolution of the patient’s lesions after 3 weeks of oral terbinafine

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Bullous tinea corporis, owing to the rarity of its presentation, can be mistaken for a variety of dermatoses such as erythema multiforme, bullous allergic contact dermatitis and linear IgA bullous dermatosis. In

fact, in one reported case, the authors empirically started treatment with dapsone for linear IgA bullous dermatosis before a change in the morphology of the lesions prompted them to send samples for direct microscopy, which returned positive for hyphae.⁴

We hope that this report of targetoid bullous tinea corporis will encourage clinicians to consider a fungal aetiology in the differential diagnoses of generalised targetoid bullous lesions in contrast to the annular scaly plaques usually expected in tinea.