Ian D. Duncan

The Pathology of Equine Laryngeal Hemiplegia

SummaryLaryngeal muscles and nerves were obtained from 42 horses, 3 of which suffered from laryngeal hemiplegia. Of the remaining 39 clinically normal horses, 30% (12) demonstrated pathological changes in the laryngeal musculature.These changes were indicative of neurogenic atrophy and varied from fibre type grouping only, to marked fascicular atrophy. The muscles affected were those on the left side of the larynx and were supplied by the recurrent laryngeal nerve. Early changes were, however, seen in the muscles on the right side in one case. The main feature of the neural lesion was a distally progressive loss of myelinated nerve fibres, but evidence of segmental demyelination and remyelination was seen in teased nerve fibre preparations. The pattern of the muscle lesion and the possible aetiology of the neuropathy are discussed.

Age changes in the dorsal and ventral lumbar nerve roots of dogs

SummaryDorsal and ventral nerve roots from clinically normal dogs aged 3 months to 13 years have been examined. The L6, L7 roots were selected and samples removed from the roots within the sub-arachnoid space and within the root sleeves. Routine light microscopy, electron microscopy and single fibre studies have been made. The single teased fibre results have been analysed statistically for the correlation of internodal length and diameter. With increasing age there was marked evidence of demyelination and remyelination. Paranodal and segmental demyelination were present and there were numerous fibres showing a marked variation in internodal length. In younger animals these features were not seen. Wallerian type degeneration was uncommon. In older animals myelin balloons, similar to those described proximal to neuromas, were commonly found. These were present in both dorsal and ventral roots. The balooning appeared to result from a splitting of the myelin sheath. The intervening space was non-staining but sometimes contained myelin debris. No evidence of neuromas was present in these roots or peripheral nerves. These studies suggest that both the ballooning and demyelination and remyelination are age related.

The central nervous system in canine giant axonal neuropathy.

SummaryThe pathology of the central nervous system (CNS) in a dog with giant axonal neuropathy (GAN) is presented. Swollen axons containing excessive and disorganised neurofilaments were present in the spinal cord, mainly at the distal portions of long tracts. The fasciculus gracilis and dorsal spinocerebellar tracts were affected only in the rostral cervical cord while the lateral cortico spinal tract was principally involved in the lower thoracic and lumbar cord. Occasional swellings were also found in the central dorsal columns of the rostral lumbar segments and in the dorsal and intermediate grey matter. The nuclei gracilis and cuneatus, restiform body and ventral spinocerebellar tracts were all involved in the brain stem. Spheroids were seen in the white matter of the rostral cerebellar vermis and in the granule cell layer. The brachium of the superior colliculus contained swollen axons and the cortex was diffusely involved with spheroids. The distribution was of a distal axonopathy and the cortical changes provided an explanation for the abnormal EEG and mental retardation found in some human patients.

A Myopathy Associated with Myotonia in the Dog

SummaryThe pathology of two cases of a canine myopathy associated with myotonia are presented. The changes were interpreted as dystrophic. The most obvious features were a rounding on cross section and variation in fibre size with numerous internal nuclei, many of which formed chains. Degeneration and regenaration were seen and there was a slight increase in perimysial and endomysial connective tissue. Only one ringed fibre was seen, but no sarcoplasmic masses. Enzyme histochemistry failed to demonstrate any selective Type I fibre atrophy. The peripheral and central nervous systems were normal in both cases.

“The central areas” of denervated canine muscle

Abstract Various denervated canine muscles have been examined using conventional stains and enzyme histochemistry. The majority contained fibres with an abnormal central area showing increased activity for the oxidative enzymes NADH and SDH. The areas also showed high activity for phosphorylase and increased amounts of glycogen. On myosin ATPase only the dark fibres appeared affected. The relationship between these changes and denervation is discussed.