Polyneuropathy and primary erythrocytosis in a cat

A 22-month-old, male, neutered, domestic longhair cat presented with a 2-month history of progressive paraparesis and severe muscle atrophy; neuromuscular dysfunction was suspected on neurological exam. A manual packed cell volume was 73%, and serial measurements following fluid therapy remained high. Investigations for secondary causes of erythrocytosis were unremarkable, so a diagnosis of primary erythrocytosis was made. Electromyography showed spontaneous activity within all tested muscles of the pelvic limbs. Motor nerve conduction velocity for the sciatic-tibial nerve was prolonged, and the compound muscle action potential measured at the hip was reduced. Phlebotomy achieved a reduction of the packed cell volume to 52%, and oral hydroxyurea was started. An improvement in the degree of paraparesis was seen 3 weeks after discharge, and this continued until the cat was normal at 4 months. Fluctuations in the packed cell volume necessitated adjustments in hydroxyurea dosage, but no relapse of paraparesis occurred during the 18-month follow-up period.