Progressive axonopathy: an inherited neuropathy of boxer dogs. Quantitative and morphometric analysis of the peripheral nerve lesion.

Previous studies have described and illustrated the lesions in the peripheral nerves in progressive axonopathy, an inherited neuropathy of Boxer dogs. The present paper assesses these changes using quantitative techniques. Cervical and lumbar nerve roots and tibial, phrenic and medial cutaneous radial nerves have been studied in affected and age-matched normal dogs aged 2 months to 3 years. The dorsal and ventral nerve roots, and to a lesser extent the proximal nerves, contain a proportion of swollen myelinated axons whereas in the middle and distal nerves the larger diameter fibres fail to develop to their expected maximum calibre. The unmyelinated axons remain the same size as those in normal dogs. Myelin sheath changes, with attenuation or loss of the sheath and/or remyelination, become increasingly prevalent through the course of the disease, always maintaining a proximal to distal decrease in their frequency. Quantification indicates that, particularly in the ventral roots, many axons have disproportionately thin sheaths with shortened internodes. Axonal degeneration and regeneration increase in frequency in the distal nerves as the disease progresses. The cervical ventral roots prove an exception in that they contain large numbers of regenerating clusters at most stages. It is suggested that in progressive axonopathy an axonal transport failure may occur in the roots leading to the axonal swellings, as a result of which a developmental hypoplasia occurs in the more distal, larger diameter fibres. The prominent, but unevenly distributed, myelin sheath changes indicate a severe disturbance in axon-sheath cell inter-relationships.