Clinical History
The dog presented for a one year history of coughing, inspiratory stridor, and a “goose-stepping” pelvic limb gait. The dog would stand with it’s stifles extended causing his hindquarters to be elevated (Fig. 1). Bronchodilators and corticosteroids had been tired but were not effective in eliminating the clinical signs.

  Fig. 1. Note the elevation of the dog’s hindquarters resulting from standing with stifles extended.

Physical and Neurological Examination
The physical examination was not abnormal for a 12 year old dog with the exception of marked inspiratory stridor.  Mentation, cranial nerves, and muscle tone were considered normal. A marked hypermetric “goose-stepping” pelvic limb gait was present with normal forelimbs. Patellar reflexes were absent bilaterally.

Diagnostic Testing

CBC: Unremarkable

Serum Chemistry: Elevated alkaline phosphatase that was likely steroid related

Thyroid: T4 performed 3 months previously was within the reference range

Thoracic Radiographs: Evidence of chronic bronchitis otherwise unremarkable

Abdominal and Spine Radiographs: No abnormalities found

Laryngeal Evaluation: The vocal folds showed an absence of abduction bilaterally during inspiration. The trachea was considered normal.

Diagnosis and Treatment
As determined by the observed laryngeal paralysis and absence of patellar reflexes on neurological examination,  a generalized polyneuropathy was suspected. An arytenoid cartilage lateralization was performed, and muscle and nerve biopsies taken with the dog under general anesthesia. Biopsies from the vastus lateralis and gastrocnemius muscles showed atrophy consistent with denervation, that was most marked in the distal limb muscle. There was marked depletion of large myelinated fibers and endoneurial fibrosis in a resin embedded biopsy from the peroneal nerve (Fig. 2). Axonal degeneration was observed in a few remaining large caliber fibers.

Clinical Course and Outcome
The surgical procedure resulted in marked improvement in breathing without resting inspiratory stridor. At a 3 month follow-up, breathing was still without difficulty. The gait abnormalities remained. This dog is an excellent example of the occurrence of laryngeal paralysis as part of a generalized polyneuropathy in an older large breed dog. In the experience of Dr. Diane Shelton of the Comparative Neuromuscular Laboratory, this is not an uncommon finding. Surgical treatment of the laryngeal paralysis usually results in marked improvement in respiration and in some cases, improved exercise tolerance. The peripheral neuropathies in most cases are slowly progressive ranging from several months to a few years. Evaluation of muscle and peripheral nerve biopsies can confirm the presence and severity of nerve fiber loss, but cannot provide a specific underlying etiology. This is still important information as the biopsies can confirm the presence of an underlying neuropathy and provide an explanation for concurrent or worsening weakness and gait abnormalities.