Spinal cord degeneration in juvenile and adult swine

Abstract

Spinal cord degeneration was identified in nine swine consisting of four fattening pigs (5 months old) and five adult sows (2 to 3 years old). These animals were raised on nine different farms and culled over a 1.5-year period on account of similar clinical signs encompassing ataxia and paresis progressing to paraplegia. Histopathologically, the spinal cord exhibited white matter degeneration with no predilection for specific tracts, which was more severe in five swine and less severe in the others. White matter lesions were characterized by Wallerian-type degeneration of myelinated axons, exhibiting axonal swelling/loss and myelin sheath dilation/disintegration associated with occasional macrophage reaction and little fibrous astrogliosis. Gray horn neurons were unremarkable. In the brain examined in three cases, similar but minimal degenerative lesions were observed in the marginal areas of the brainstem in one case. Significant lesions were absent in the hind limb nerves, including sciatic nerve, femoral nerve, and obturator nerve, in seven cases. The spinal lesions were regarded as being a variant of neurodegenerative disorder. The pathogenesis appeared to involve a primary impairment of myelinated axons in the spinal white matter (central axonopathy). The pattern and extent of this disease were considered different from those reported previously in swine with neurodegenerative or myelinopathic disorders of inherited, toxic, or nutritional origin. The etiology remains unknown, though a metabolic abnormality was suspected to be one of the likeliest possibilities.