[Perforating granuloma annulare with transfollicular perforation].
INTRODUCTION: The perforating granuloma annulare is a rare form of granuloma annulare. The clinical diagnosis is difficult and the confirmation is histological. The localisation is unique in less than 10% of all cases. We report a documented case with a histological suspicion of transfollicular perforation. OBSERVATION: A 36 year-old woman, without any particular antecedent, presented on her upper arm a single ulcerated nodular lesion that had evolved for one year. The clinical examination and biological investigations were normal. The histological examination led to the diagnosis of perforating granuloma annulare with a large epidermic ulceration. Treatment with a topical corticosteroid was disappointing and the removal was decided. DISCUSSION: In our observation, the single localization of this lesion raises the problem of differential diagnosis such as cutaneous tuberculosis, atypical mycobacteriosis, skin sarcoidosis, foreign body granuloma, epidermoid carcinoma or perforating dermatitis. The histological examination permitted diagnosis of a perforating granuloma annulare with large epidermic ulceration. The infiltration and destruction of a hair follicle evoked the possible transfollicular elimination of the necrotic material. Other pathologies with the histological aspect of a palisading granuloma were excluded from this context. No associated pathology such as diabetes nor any other favouring factors such as ultraviolet light or insect bites or traumas were identified. The physiopathology of perforating granuloma annulare and the process of perforation remain unknown. Numerous therapies have been proposed with variable results.