Pathology showed muscle fiber atrophy and intracytoplasmic nemaline rods. The authors are quick to point out that the presence of nemaline rods alone is insufficient for a diagnosis of nemaline myopathy . These structure rarely may be seen in a number of other neuromuscular disorders, including mitochondrial myopathies, polymyositis, spinal progressive muscular atrophy, and acute alcoholic myopathy. An accurate diagnosis requires the presence of large numbers of nemaline rods in a symptomatic patient, as well as the absence of findings typically seen in other myopathies . Staining of cryostat sections by the modified Gomori trichrome technique is the best method for detecting the rods, which appear purple or red against the blue-green myofiber background.
Rods show a tendency to cluster under the sarcolemma and around nuclei.
The proportion of fibers containing rods varies from case to case and from muscle to muscle. There is often marked type 1 fiber predominance, but a disproportion in fiber size, with type 1 fibers being small and type 2 fibers being large or normal. Electron microscopy reveals accumulation of the rods with localized enlargement and streaming of the Z lines. The rods appear to arise from the Z disks. Also, like the Z disks, the rods are contiguous with thin filaments.