Stringhalt in horses: a distal axonopathy.

A detailed investigation of the neuropathology of a horse affected with stringhalt was performed. Qualitative and quantitative light and electron microscopy, and single teased fibre preparations of peripheral nerve demonstrated predominantly axonal degeneration, the stage of which was appropriate for the duration of clinical signs. There was selective involvement of large myelinated nerve fibres. A proximal to distal increase in the severity of pathological changes was present in the peripheral nerves. The long left recurrent laryngeal nerve was the most severely affected, followed in order by its right counterpart, the hindlimb and forelimb nerves. Neurogenic atrophy of muscles innervated by affected peripheral nerves also showed a distally graded increase in severity. No lesions were observed in the central nervous system. It was concluded that this disease should be classified as a distal axonopathy.