Primary localized cutaneous amyloidosis.

A 61-year-old man presented for evaluation of a bruise-like lesion of the right knee. He was found to have an ill-defined, light brown patch with focal areas of dark red and brown. The histopathologic diagnosis was consistent with amyloidosis. Further subtyping showed that the amyloid protein was AL (κ). A systemic evaluation failed to show internal involvement. Amyloidosis comprises a spectrum of diseases, which range from systemic to localized cutaneous types, and is characterized by the extracellular deposition of amyloidosis protein as beta-pleated sheets. The forms of amyloidosis are differentiated by the specific types of protein-derived amyloidosis fibers. Both nodular and primary systemic amyloidosis can present as nodules on the skin owing to deposition of AL type amyloid protein. Primary systemic amyloidosis, which carries a poorer prognosis than does nodular amyloidosis, also may give rise to ecchymoses and many other cutaneous and extracutaneous findings. Histopathologic features are similar in both cases and involve the deposition of amorphous, eosinophilic material in the dermis. Nodular amyloidosis may progress to primary systemic disease in up to 50% of cases. Because our patient had no systemic involvement and the lesions did not appear nodular in nature, the patient was given a diagnosis of primary localized AL cutaneous amyloidosis. Routine follow-up for this patient is necessary to detect any potential disease progression.