[A representative case of joint contracture as a main feature of AL amyloid deposits identified in the skeletal muscles].

A 68-year-old man, with a history of type 2 diabetes mellitus and chronic kidney impairment, had been suffering from progressive knee joint contracture and dysesthesia of the lower extremities for 4 years. When he walked, his knees remained bent owing to contracture of the knee joints. There was no evidence of muscle pseudohypertrophy, intramuscular nodules, or muscle weakness. Clinical examination revealed IgA λ M-protein, reticular high-signal intensity lesions demonstrated by magnetic resonance T2-short TI IR(STIR) imaging of the lower extremity muscles, and a mixture of neurogenic and myogenic changes demonstrated by needle electromyography. A biopsy specimen from the vastus lateralis muscle identified Aλ amyloid deposits around the vessels, establishing a diagnosis of amyloid myopathy based on systemic AL amyloidosis. This case demonstrated that joint contracture and reticular lesions shown by magnetic resonance STIR imaging of the muscles can alert the physician to consider muscle biopsy to investigate deposition of amyloid in the skeletal muscles even in the absence of muscle pseudohypertrophy or weakness, both of which are characteristic of amyloid myopathy.