Mitochondrial myopathies usually have a chronic course of progressive limb weakness, exercise induced myalgia without muscle tenderness, and normal or only mildly raised serum creatine kinase.1 Acute or subacute presentation or exacerbation of nervous system signs is common in Leber’s hereditary optic neuropathy (LHON) and in mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes (MELAS),1 but has not been reported for muscle in mitochondrial diseases. We describe a patient who presented with rapidly progressive, subacute muscle weakness due to a mitochondrial disorder.

A 38 year old woman presented for the first time with a sudden rapid progression over six weeks of myalgia at rest and muscle weakness. She became bedridden just before admission. On questioning she reported that for about a year she had some muscle pain and a very mild weakness, but continued with all her chores as a mother of six children.

Physical examination disclosed diffuse and pronounced muscle tenderness and moderate to severe proximal limb weakness (3/5 on the MRC scale), with normal strength distally. Tendon reflexes were hypoactive. She had no pyramidal signs and her mental functions, cranial nerves, sensation, and cerebellar functions were intact. The following laboratory tests were normal or negative: …