Affected-dogs are bright and alert, although often poorly muscles when compared with their normal littermates. Temporal muscle atrophy is often a feature, but cranial nerve functions are otherwise normal. Muscle tone may be normal or reduced. There is no muscle pain on palpation nor dimpling on percussion. Severely affected pups are obviously weak and may have difficulty wheelbarrowing or hopping, although in less severely affected pups, postural testing may indicate no abnormalities.
Proprioceptive function is normal and no sensory deficits have been observed in affected dogs.
Tendon reflexes are generally reduced or absent, even in midly-affected dogs with little muscle atrophy. There is no impairment of bladder function nor other signs of autonomic nervous system dysfunction. A diagnosis of HMLR may be suspected from the signalment data, clinical signs, and results of the neurological examination. Further procedure used in establishing the diagnosis include serology, electrodiagnosis, and muscle biopsy. Serum creatine kinase may be within normal limited or may be moderately elevated.