Pathological aspects of Australian Stringhalt

Area of Science:

• Veterinary Pathology
• Neuropathology
• Equine Medicine

Background:

• Australian Stringhalt is a debilitating neurological condition in horses.
• Previous studies have indicated neuromuscular involvement, but detailed pathological findings are limited.

Purpose of the Study:

• To conduct a detailed pathological examination of tissues from horses with Australian Stringhalt.
• To characterize the specific lesions in peripheral nerves and muscles.
• To investigate the potential mechanisms underlying the observed pathology.

Main Methods:

• Post-mortem examination of nine horses with clinical Australian Stringhalt.
• Histopathological and morphometric analysis of peripheral nerves (including superficial peroneal, deep peroneal, distal tibial, plantar digital, volar, and recurrent laryngeal nerves).
• Histochemical evaluation of specific muscles (long and lateral digital extensors).

Main Results:

• Lesions were confined to peripheral nerves and muscles, with selective loss of large diameter myelinated axons in affected nerves.
• Observed nerve changes included demyelination, fibrosis, and onion-bulb formation.
• Significant muscle atrophy and fibrosis were noted, particularly in the long and lateral digital extensors, with a reduction in type II fibers.

Conclusions:

• The pathological findings are consistent with a distal axonopathy leading to neurogenic muscle atrophy in Australian Stringhalt.
• The distribution of lesions suggests susceptibility of longer, larger myelinated nerve fibers to injury.
• The underlying cause of this distal axonopathy in Australian Stringhalt remains unidentified.