The giant axonal neuropathy--clinical and hisotological aspects, differential diagnosis and a new case.

The giant axonal neuropathy (GAN) is morphologically characterized by axonal swellings and accumulations of neurofilaments in giant axons and other cell types. Curly hair is not a constant finding. The clinical course is progressive and mostly starts in early childhood. We report the case of a boy aged 6 years at the time of sural nerve and muscle biopsy. Suralis nerve showed a reduced numerical density of myelinated fibres with a consecutive endoneural fibrosis. Morphometric investigation revealed a pronounced reduction of fibres measuring 8-12 microm in diameter. Giant axons were seen in relatively low number and were not very large with a maximum diameter of 18 microm. They had a relatively thin myelin sheet proved also by the high G ratio in the histogram. Many onion bulb formations of Schwann cells were present. There are only few reports of giant axons with such low maximum diameter in cases with GAN, the lowest maximum diameters being reported in case reports on Japanese children. Up to now, this is the first report of a non-Japanese patient with a low maximum diameter of giant axons of less than 20 microm in peripheral nerve biopsy. Ultrastructurally, typical accumulations of neurofilaments and osmiophilic aggregates were found in giant axons. Other diagnoses with occurrence of giant axons could be excluded in view of the absence of specific findings. Sporadic or familial cases with giant axons are discussed. Sceletal muscle biopsy (M. quadriceps femoris) showed neurogenic affection with presence of small angulated atrophic muscle fibres.