Chronic relapsing demyelinating encephalomyelitis associated with persistent spontaneous canine distemper virus infection.

This is the first report of spontaneous canine distemper virus (CDV) infection in a dog associated with chronic progressive multiphasic neurological disease. Initial neurological deficits in the pelvic limbs progressed rapidly to paraplegia with almost complete remission after 9 weeks. Then another acute episode occurred with severe thoracic limb deficits and cerebellar dysfunction and progressive neurological deterioration over 3 months with rising serum neutralizing (SN) anti-CDV titers in the serum and cerebrospinal fluid (CSF). Three neuropathologically distinct lesions of spinal cystic necrosis, chronic demyelinating foci in the cerebellum and acute demyelinating encephalitis in the pons were identified. Persistent CDV antigen was demonstrated immunocytochemically only in acute lesions and atypically restricted to neurons. However, the immunological mechanism associated with the distinct remissions and exacerbations and CDV antigen clearance from chronic demyelinating lesions but persistence in acute lesions, despite a vigorous anti-CDV serologic response, was not defined.