Amyloid myopathy: evidence for mechanical injury to the sarcolemma

Myopathy is a rare clinical manifestation in primary systemic amyloidosis. The clinical phenotype and muscle histology are well described but the pathophysiological mechanisms remain poorly understood. We report a 40-year-old man who presented with hypertrophic cardiomyopathy and a limb girdle syndrome associated with deposition of amyloid and free lambda light chains in skeletal muscle. Electron microscopy showed amyloid fibrils, physically disrupting the plasma membrane and basal lamina, while laminin immunocytochemistry revealed a reduction of laminin beta1 and upregulation of laminin alpha1. We believe that one of the possible pathophysiological mechanisms in amyloid myopathy is mechanical disruption of the sarcolemma by the abutting amyloid fibrils.