Hyaline body myopathy.

Muscle biopsy from two unrelated patients, a male aged 40 and a female aged 3, with relatively non-progressive limb weakness since infancy, revealed numerous subsarcolemmal glassy, hyaline appearing bodies present in 20-30% of the fibres. Type 1 fibre predominance was present, and the hyaline bodies were exclusive to type 1 fibres. The hyaline bodies were negative with oxidative enzyme and periodic acid-Schiff stains. Electron microscopy showed the hyaline bodies to contain amorphous granular material of unknown composition. No membrane separated the hyaline bodies from the surrounding sarcoplasm. Hyaline body myopathy most likely represents a distinct congenital myopathy because of its childhoot-onset, non-progressive course, and distinct morphological features.