P.412 - Diagnostic implications of three cases of skeletal muscle light-chain (AL) amyloidosis

Abstract

A 70-year-old female with a two year history of painless, progressive proximal weakness and markedly elevated CK (>1600 U/l), a 74-year-old male with a year's history of exercise-induced myalgia, including claudicatio masticatoria and fatigue with CK in the normal range and a 79-year-old male with a four month history of myalgia, constipation and weight loss with elevated CK were diagnosed with skeletal muscle amyloidosis by Congo red stain on muscle biopsy samples. They had IgG lambda, IgA lambda and IgG kappa light chain paraproteins, respectively. In the first and third case, sural nerve biopsies showed some, predominately axonal damage, but no amyloidosis. Rectum biopsy in the second as well as colon and gastral biopsy in the third case failed to detected amyloid deposition, too. In case one, the diagnosis of °I plasmocytoma and in case three of suspected multiple myeloma had been established, but prior to the diagnosis of amyloidosis, no treatment was considered necessary. In the second case, the paraprotein was discovered at the time of biopsy. In every case, muscle biopsy showed some aspects of neurogenic damage and nerve conduction studies revealed some abnormalities. In case one, deposition of congophilic, birefringent material was solely vascular, while in case two and three there was some deposition surrounding muscle fibres. In case three only, immunohistochemistry showed activated complement (C5b9) colocalised with amyloid deposition, widespread capillary changes and perimysial pathology. All the clinical and biopsy findings in these cases are in line with the literature. Nerve, rectum and possibly labial salivary gland biopsies are generally considered to have a higher detection rate for amyloidosis. However, we conclude that biopsy analysis of clinically affected muscle should be the standard procedure in patients with muscular complains and paraprotein. A non-conclusive biopsy of another tissue cannot be accepted as a substitute.