A new concept of childhood nemaline myopathy.

Abstract

Two patients with congenital nonprogressive muscle weakness had marked accumulation of typical rods in virtually every extrafusal muscle fiber on biopsy. One patient died at age 41/2 years, and profound rod accumulation was confirmed in five skeletal muscles postmortem. Unusual histochemical features were the virtual absence of type II extrafusal muscle fibers (biopsy of both patients), two normal histochemical types of intrafusal fibers, lack of definite rod accumulation in intrafusal muscle fibers and myocardium, and targets and central cores in muscle fibers of diaphragm in coexistence with rods. These can be explained by a disturbed alpha motor neuron innervation in the face of normal innervation of the spindles. Abnormal innervation of extrafusal fibers may have a direct pathogenic role in rod formation. This departs from the generally held concept that congenital nemaline myopathy is a primary disease of skeletal muscle. Key Words.— Nemaline; rod; myopathy; central cores; targets.