[Diagnostic muscle MRI abnormality in a patient with inclusion body myositis]

A 64-year-old woman was admitted to our hospital because of muscle weakness and atrophy in the extremities. Four years before admission, he was noticed to have elevated creatine kinase (CK) level, but had no further evaluation. Two years later, she became difficult in standing up and needed a wheelchair. Six months before admission, she noticed muscle wasting in the buttock, thigh, bilateral forearms, and weakness in the upper limbs. On neurologic examination, she had weakness in sternocleidomastoid and all limb muscles, predominantly in the distal portion of the upper extremities. Laboratory study revealed elevated CK, LDH, and aldolase levels, and myogenic change with fibrillation on needle EMG. Muscle biopsy showed myopathic changes with infiltration of mononuclear cells and rimmed vacuoles. The clinical manifestations as well as poor response to corticosteroids therapy were supportive of the diagnosis of inclusion body myositis. However, the distribution of muscle weakness in her wrist, weaker in the extensors than in the flexors, was not characteristic to IBM. This problem was solved by the right forearm MRI which showed a high signal intensity area in flexor muscles, but not in extensors on T1 and T2 weighted images. Accordingly, the muscle MRI of forearm was a diagnostic aid of IBM in this patient.