Internalised capillaries, neuromyopathy and myalgia.

Internalised capillaries are described in the muscle fibres of two adult males who complained of exertional myalgia. In one patient, "bundles" of internalised capillaries were found in 2% of the Type 1 fibres and many of the Type 1 fibres exhibited non-specific cytoarchitectural changes. The other had hereditary motor and sensory neuropathy (HMSN) Type 2 and his muscle biopsy exhibited the more conventional single and double internalised capillaries in 3% of the muscle fibres in addition to the anticipated neuropathic changes. Electron microscopy revealed the presence of paracrystalline inclusions in the mitochondria of muscle of both patients. Dystrophin was normal on both immunogold/silver staining and immunoblotting. Sixty five of 77 recorded patients with evidence of internalisation of capillaries have been males and 10 are known to have complained of muscle cramps or severe myalgia. An ischaemic pathogenetic predisposition is proposed as a possible stimulus to the capillary internalisation, formation of paracrystalline mitochondrial inclusions and myalgia.