JUVENILE-ONSET DISTAL MYOPATHY IN ROTTWEILER DOGS

Two juvenile Rottweiler siblings were presented with the complaint of decreased activity and various postural abnormalities, including plant igrade and palmigrade stance and splayed forepaw digits. The neurologi c examinations were otherwise normal. Electromyography revealed rare f ibrillation potentials and positive sharp waves. Motor nerve conductio n velocities were normal, whereas compound muscle action potentials fr om the interosseous muscles were decreased. These findings were consis tent with a primary myopathy. A 3rd pup from a different litter and a 4th pup from a litter with 3 of 8 affected dogs had similar clinical p resentations. Histopathologic changes in fresh-frozen muscle biopsy sa mples were similar in all pups and consisted of myofiber atrophy with mild myonecrosis, endomysial fibrosis, and replacement of muscle with fatty tissue. These changes were more severe in distal muscles than in proximal muscles. Plasma carnitine concentrations (total and free) we re decreased in all pups. Muscle carnitine concentrations (total and f ree) were decreased in 3 of 3 pups and the least affected pup had a bo rderline low free muscle carnitine concentration. Abnormalities involv ing major metabolic pathways were not found on quantification of organ ic and amino acids. Dystrophin immunocytochemistry was normal in 2 dog s tested. Distal myopathies in humans are classified under the dystrop hic group of muscle disorders. These 4 cases represent a form of muscu lar dystrophy apparently not previously reported in dogs.