Extranodal NK/T-cell Lymphoma Mimicking Granulomatous Myositis

Extranodal NK/T-cell lymphoma (ENKTL) is an aggressive non-Hodgkin lymphoma that typically develops in the upper aerodigestive tract. We encountered an ENKTL patient who presented with generalized muscle weakness with eyelid swelling, diplopia, and facial edema. A muscle biopsy revealed lymphocytic infiltration without significant atypia; some lymphocytes formed granuloma-like structures. Although the initial response to steroids was encouraging, an ulcerative eruption appeared in the thigh, and a skin biopsy revealed lymphocytes with atypia. A re-analysis of the muscle biopsy with additional immunohistochemistry revealed neoplastic NK/T lymphocytes in the granulomatous structures. Our case highlights the significance of re-evaluating muscle biopsy specimens in cases of atypical myositis.