Mitochondrial disease mimicking polymyositis: a case report.

The authors report on a 34-year-old woman who had developed severe weakness and reduction in grip strength in both upper and lower limbs. Laboratory blood tests revealed increased levels of muscle enzyme. The presence of progressive bilateral ptosis and external ophthalmoplegia raised the suspicion of a mitochondrial disease, subsequently confirmed by deltoid biopsy and genetic analysis of mitochondrial DNA that showed a deletion indicative of Kearns-Sayre syndrome. In this report we emphasise the need for a differential diagnosis between myositis and other myopathies, particularly the mitochondrial ones.