Tinea Pseudoimbricata

Abstract

A woman in her 40s presented to the dermatology department for an evaluation of a pruritic eruption on her back of 5 months duration. She was systemically well, and prior treatment had included topical corticosteroids (mometasone furoate, 0.1%, cream) with subsequent worsening of symptoms. Physical examination revealed multiple erythematous to hyperpigmented plaques comprising concentric rings with associated scale on the upper back (Figure). On further questioning, she disclosed that her 3 children had all been recently treated for tinea capitis.Direct examination of a potassium hydroxide preparation failed to reveal hyphae. A mycological culture revealed Microsporum andouinii. The final diagnosis was tinea corporis of the pseudoimbricata type. Treatment with a 6-week course of oral griseofulvin (500 mg, twice daily) resulted in complete resolution of the lesions with only postinflammatory hyperpigmentation.Tinea pseudoimbricata is a rare subtype of tinea usually caused by Trichophyton tonsurans, Trichophyton mentagrophytes, and some Microsporum species. The name derives from its resemblance to tinea imbricata, an endemic fungal infection of the Southwest Pacific, Central and South America, and Southeast Asia that is caused by Trichophyton concentricum. 1 The ring-within-a-ring appearance, sometimes widespread, can also be confused with erythema gyratum repens. 2 This appearance has been associated with local or systemic immunosuppression, which is frequently associated with the erroneous use of topical corticosteroids. The inhibition of a person's immune response could induce intermittent inflammatory reactions against the dermatophyte, which are responsible for the appearance of the concentric erythematosquamous rings. 3 The treatment of tinea pseudoimbricata relies on long-course oral antifungal treatments, as topical antifungal agents are usually not sufficient. 2,4 This case highlights 2 issues: the first underlines that although a potassium hydroxide preparation is easy to perform and an inexpensive diagnostic method, its sensitivity is often low and interpreter dependent. A superficial or punch biopsy can readily identify the presence of fungal structures using a periodic acid-Schiff staining. However, only a mycological culture or polymerase chain reaction test can identify the specific causative fungus. The second stresses the importance to examine all the relatives of the same household.