[Patient of myofibrillar myopathy associated with muscle cramp and distal muscle involvement].

A 53-year-old man presented mild, but gradually worsening, distal-dominant upper bilateral limbs weakness and muscle cramp in both legs from the age of 30. He had no obvious muscle atrophy during the course of the disease. Muscle biopsy of the right lateral vastus muscle showed myopathic changes with round or helical hyaline inclusions in eosinophilic on H&E staining and dark green on modified Gomori trichrome. There were also non-rimmed vacuoles. NADH-TR showed lack of enzymic activity in areas corresponding to the inclusions. Immunohistochemistry demonstrated abnormal accumulation of desmin and myotilin in fibers with inclusions. Given these pathological findings, he was diagnosed with myofibrillar myopathy (MFM). Because MFM is genetically heterogeneous, its clinical manifestations are reported as variable. While MFM patients are sometimes reported to develop serious conditions such as severe weakness, cardiomyopathy or respiratory failure, which require a pacemaker or mechanical ventilator, our case only had mild distal dominant limb weakness and muscle cramps. Our patient suggests that we must consider MFM as a differential diagnosis in adult onset distal myopathies.