Human T cell lymphotropic virus type-1 associated lymphoma presenting as an intramuscular mass of the calf

Adult T cell leukemia/lymphoma (ATLL) is a mature T cell neoplasm caused by the human oncogenic retrovirus human T lymphotropic virus type-1 (HTLV-1). While several musculoskeletal manifestations have been described in ATLL, skeletal muscle involvement is unusual, with only four cases reported in the English-language literature. We present a rare case of ATLL manifesting as an intra-muscular calf mass in a 58-year-old man who immigrated to the USA from West Africa. While skeletal muscle involvement by lymphoma is uncommon, it remains important to consider within the differential diagnosis when there are suggestive imaging findings because it entails important technical biopsy considerations as well as treatment implications. This case report also raises awareness of ATLL presenting outside of typical HTLV-1 endemic areas, related to current population migration patterns. ATLL should therefore be considered in patients with appropriate risk factors.