Distal and myofibrillar myopathies

Abstract

The distal and myofibrillar myopathies are two heterogeneous groups of inherited or sporadic primary and progressive muscle disorders. Distal myopathy is a clinical concept with predominant distal muscle weakness and atrophy in the hands, forearms, lower legs, or feet. Myofibrillar myopathy is a muscle pathology concept with findings consisting of dark and hyaline cytoplasmic changes on trichrome stain, abnormal protein aggregations, disintegrated myofibrillar structures and rimmed vacuoles. This chapter adopts a clinical and differential diagnostic approach and some novel forms of distal myopathy are described. Molecular genetics discoveries during the last 20 years have greatly advanced our understanding of these disorders and a specific chromosomal localization is known for all clinically described entities. The gene and its protein product have been identified for over 20 different myopathies. Many patients with a pathological diagnosis of myofibrillar myopathy clinically show a distal phenotype so these categories are presented together in this chapter.