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 λ 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 β₁ and upregulation of laminin α₁. We believe that one of the possible pathophysiological mechanisms in amyloid myopathy is mechanical disruption of the sarcolemma by the abutting amyloid fibrils.