Childhood-onset anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase (anti-HMGCR) necrotizing myopathy needs to be...

A 24-year-old woman visited our hospital with a complaint of walking disability. She had no family history of consanguineous marriage, and her developmental history was unremarkable, with good physical performance just before the onset. At the age of 13, she developed difficulty in walking and visited a pediatrician. Her serum CK level was 10,000 IU/l and she was diagnosed with muscular dystrophy by muscle biopsy. At the age of 16, she became wheelchair dependent and was admitted to our hospital. Physical examination revealed diffuse muscle atrophy and proximal weakness, with no calf hypertrophy or selectivity of muscle involvement. Needle EMG and MR images indicated inflammatory myopathy. Muscle biopsy revealed necrotic and regenerating fibers and lymphocyte infiltration. She was re-diagnosed with inflammatory myopathy and recovered walking capacity after immunotherapy. Subsequently, she was tested positive for anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) antibodies. To distinguish treatable inflammatory myopathy from muscular dystrophy, a comprehensive assessment of patient history, family history, selectivity of muscle involvement, findings suggestive of inflammation in EMG and CT/MR imaging, and muscle pathology is necessary.