Comparative Neuromuscular Laboratory

NEUROMUSCULAR CASE OF THE MONTH - SEPTEMBER 2006

Reversible Megaesophagus Associated with Atypical Addison’s Disease in a 4 year old Male Standard Poodle
Contributed by Dr. Andrew Bidwell
Germantown Veterinary Clinic
Germantown, MD

Clinical History
A 4 year old male neutered Standard Poodle presented for a 5 day history of hacking cough and choking. The owner commented that “something was caught in the throat”. The dog had also been “vomiting” into his mouth for 3 weeks and swallowing it, usually while laying down. The dog was on cefpodoximine proxetil (Simplicef™, Pfizer Animal Health) once daily for pyoderma, and had been previously treated by a dermatologist for skin allergies.

Physical and Neurological Examination
Mild to moderate dental tartar and staining was noted. An intermittent grade 1-2 out of 6 systolic heart murmur was present on the left chest wall. No cough was elicited on tracheal palpation, and oral and pharyngeal examination was normal rostral to the larynx. Skin crusts were located on the left medial metatarsals. The remainder of the physical and neurological examinations was unremarkable.

CBC – within the reference range
Electrolytes including Na, K, and Cl - within the reference range with Na:K 35:1
Thyroid panel – performed at Michigan State University not indicative of primary thyroid disease. Negative for thyroglobulin autoantibodies

Acetylcholine receptor antibody titer – 0.12 nmol/l (canine reference <0.6 nmol/l)

Thoracic radiographs – A large dilated esophagus was found containing food (Fig. A). The lungs were normal. The large esophagus was confirmed with oral administration of Renograffin (Fig. B).

Diagnosis and Outcome
A diagnosis of megaesophagus secondary to Atypical Addison’s disease was made. The original complaint of “vomiting” by the owner was actually regurgitation secondary to the megaesophagus. The dog was started on prednisone (5 mg PO SID) with plans to evaluate again in 2 weeks. At the 2 week follow-up, the owner reported that, with the exception of PU/PD from the prednisone, the dog was acting like a puppy again. At a 4 week follow-up, repeat thoracic radiographs showed resolution of the megaesophagus (Fig. C). The prednisone dosage was decreased (1.5 mg PO SID) due to PU/PD and abnormal behavior. The dog continues to do well.