"Clinical and neuropathological findings of Equine Motor Neuron Disease in two italian horses"

Two Italian saddle horses, a 10 year old gelding and a 14 year old mare, were admitted with a complain of progressive weight loss and weakness, resulting in excessive lying down on the floor of their box. Appetite was good and micturition and defecation normal. The general physical examination was normal. The horses underwent a complete neurological examination, cell blood count (CBC), and biochemical profile. Vitamin E plasma levels were not measured because of previous supplementation. Muscle and nerve biopsies were taken from the left sacrocaudalis dorsalis medialis muscle and the ventral branch of the left spinal accessory nerve, respectively. Immediately after euthanasia for humane reasons, cerebrospinal fluid (CSF) was collected and examined and both horses had a neuropathologic examination of the brain and spinal cord. Samples of the left radial and peroneal nerves were also examined in one horse and an electromyographic (EMG) examination was performed under general anaesthesia on the second horse. Abnormal neurological examination findings were severe generalised muscle atrophy with marked muscle tremors of the antigravitational muscles when the horses were forced to stand, and frequent shifting of the weight from limb to limb. One horse had an abnormal low carriage of the head. Gait was characterised by moderate tetraparesis with hypometria of the four limbs and exercise intolerance. There was no evidence of ataxia. BC, biochemical profile and CSF examination were normal. The EMG showed fibrillation potential in the paravertebral muscles. Pathological findings were similar in both cases: scattered neuronal degeneration and loss in the ventral horns of the spinal cord and in the caudal brain stem. Affected neurons were swollen and chromatolytic, and occasionally showed intracytoplasmic eosinophilic inclusions. Some degenerating motor neurons were shrunken, sometimes with fragmenting nucleus. Small microglial nodules were also observed at the sites of neuronal loss. PAS-positive and Luxol fast blue-positive ceroidal lipopigment granules were observed in the cytoplasm of many degenerating neurons and some endothelial cells in the affected areas. Occasional perivascular accumulation of macrophages laden with residual ceroidal pigment was also noticed. Examination of spinal accessory, peroneal and radial nerves showed loss of large diameter fibres and axonal degeneration characterised by axonal swelling, myelin ovoids formation and phagocytosis by macrophages. Scattered angular myofibres and occasional hypertrophic fibres were observed in the sacrocaudalis dorsalis medialis muscle.