Clinical History
A 10-month-old male neutered Pit Bull terrier (Fig. 1) was presented for a clumsy gait since obtained by the owner at 6 weeks of age. Progressive weakness and a change in bark were noted for 3 months prior to presentation. Two weeks prior to presentation, surgery was performed for an elongated soft palate since the dog would “vomit” after drinking water. 

Figure 1

Physical and Neurological Examination
No specific abnormalities were found on physical examination. On neurologic examination, exercise intolerance and a high-steppage pelvic limb gait that became short-strided was noted (Go to Video Clip). Conscious proprioception was slightly decreased in all limbs and all spinal reflexes were decreased. The cutaneous trunci reflex could not be elicited. Although cranial nerve examination was normal, a bark change was obvious (Go to Video Clip).  Neuroanatomical localization was to the neuromuscular system.

Diagnostic Testing
Routine laboratory testing -  A complete blood count and serum chemistry panel (with serum creatine kinase activity) was within the reference range. Acetylcholine receptor antibodies were not detected and a T4 was within the reference range.  

Electromyography (EMG) – Anesthesia for EMG consisted of induction with diazepam and propofol, and maintenance with 2-3% isoflurane. Spontaneous activity included increased insertional activity, fibrillation potentials and positive sharp waves only in muscles distal to the elbow and stifle with the exclusion of the gastrocnemius.

Muscle and nerve biopsies – A biopsy from the cranial tibial muscle showed a pattern of atrophy consistent with denervation. A resin embedded biopsy from the peroneal nerve showed marked depletion of myelinated nerve fibers of all calibers, scattered inappropriately thinly myelinated fibers and occasional onion-bulb formations (Figs. 2-4, toluidine blue stain).

Figure 2

Figure 3

Figure 4

Conclusion
This 10-month-old dog is affected with a congenital distal polyneuropathy of the Charcot-Marie-Tooth or Hereditary Motor and Sensory Neuropathy (HMSN) group described in humans. There are many varied clinical forms and molecular genetic varieties described in humans but, to date, they are poorly characterized in dogs. No specific treatments are currently available.