Soft tissue amyloidoma of the extremities: report of a case and review of the literature.

Amyloidoma (tumoral amyloidosis) is defined as a solitary localized tumorlike deposit of amyloid, in the absence of systemic amyloidosis. Amyloidoma is the least common presentation of tissue amyloid deposition and may be of AL-type or AA-type. It has been reported in many anatomic sites including the respiratory, genitourinary, and gastrointestinal tracts, as well as internal viscera, the central nervous system, skin, breast, and soft tissues. Amyloidoma of soft tissues is extremely rare and occurs mainly in the mediastinum and abdomen. Soft tissue amyloidoma of the extremities is even more uncommon and, when strictly defined, only 11 such cases are reported in the English language to date. Most have been of AA-type and have occurred on the leg. Some have been associated with local trauma, surgery, infection, or peripheral vascular disease, and a few patients have been diabetic. We report the case of a soft tissue amyloidoma on the leg of an 85-year-old woman. Clinically, it was a subcutaneous nodule on the left shin, of approximately 4 years duration. Traumatic fat necrosis was suspected. On excision a firm gray/tan, lobulated, soft tissue mass, measuring 2.3 cm in greatest dimension, was observed. At the microscopic level, it was seen to consist mainly of amyloid, associated with a giant cell granulomatous reaction, a patchy lymphocytic infiltrate, and focal microcalcification. The features were those of a soft tissue amyloidoma of the extremity. Persistence of congophilia after pretreatment with permanganate in this case suggested the presence of AL amyloid.