Mitochondrial myopathies

Mitochondrial respiratory chain dysfunction is a potent cause of disease. Where once it was the realm of the interested neurologist only, mitochondrial disease is now common and may present to any and indeed all of the medical and surgical specialties.

The term mitochondrial myopathy is used as the descriptive term for this group of disorders where muscle disease is an important manifestation, albeit one that is rarely found in isolation. Classic phenotypes include Kearns-Sayre syndrome, chronic progressive external ophthalmoplegia, MELAS, MERRF, and Leber's optic atrophy. These disorders result from mutations of the mitochondrial genome (mtDNA), which encodes 13 respiratory chain proteins. More recently, genetic defects involving proteins not encoded by mtDNA have also been identified—for example, in Friedreich's ataxia, one form of hereditary spastic paraplegia, and an infantile cardiomyopathy.

The range, diagnosis, and investigation of mitochondrial disease, with particular reference to neurological manifestations, are reviewed.

Inflammatory myopathies

Introduction: The classification of this rather disparate group of conditions is reviewed. The commonest are the idiopathic inflammatory myopathies, comprising polymyositis (PM), dermatomyositis (DM), and inclusion body myositis (IBM). They enter into the differential diagnosis of other neuromuscular conditions and incorrect or late diagnosis is common. This may have two consequences. PM and DM are treatable conditions and failure to recognise them may deny the patient effective therapy. Conversely, misinterpretation of pathological changes in other disorders—notably, some forms of limb girdle muscular dystrophy—may result in inappropriate and damaging steroid therapy. Inclusion body myositis is unresponsive to treatment and probably has a different pathogenesis to PM and DM and it is described separately

Clinical features (PM and DM): Proximal weakness is always greater than distal, but the highly selective involvement of specific muscles characteristic of the muscular dystrophies is not seen. The onset may be acute (in DM) or chronic, sometimes over years (in PM). Except …