Pseudoneoplastic lesion of erythema elevatum diutinum

BACKGROUND: Erythema elevatum diutinum is a rare, chronic and recurrent dermatosis affecting adults. The disease is characterized by symmetrical, red, brownish-purple, and yellow papules, plaques, and nodules distributed mainly over the extensor surfaces of the extremities. The aetiology is unknown. The condition can occur in association with haematological malignancies (30%), and most frequently with IgA monoclonal gammapathy. Histological diagnosis is sometimes difficult, especially in the late stages of the disease. We describe an unusual case of erythema elevatum diutinum with clinical and histopathological pseudoneoplastic features. CASE REPORT: A 60-year-old man with no significant medical history consulted for a large nodule of the left knee measuring 2.5cm and red-purple papules symmetrically distributed on the extensor surfaces. Surgical removal of the nodule was performed. The histologic findings were characterized by a predominant concentric fibrosis forming well-circumscribed dermal nodules, composed of small aggregates of spindle cells with palisading and lamellar patterns. Within the nodules, pycnotic polymorphonuclear leucocytes were observed. The nodules were surrounded by a lymphoplasmocytic and histiocytic infiltrate. The diagnosis of erythema elevatum diutinum was thus made and dapsone given, with partial improvement of the lesions. DISCUSSION: This case illustrates the nodular pseudoneoplastic presentation and the difficulty of histological diagnosis, since long-standing lesions can mimic connective tissue tumours. Clues for histopathological diagnosis are neutrophils scattered throughout the lesion, sometimes associated with vasculitis. Extensive investigation should be made for polymorphonuclear leucocytes that are always present, even in late fibrotic lesions.