NEUROMUSCULAR CASE OF THE MONTH - AUGUST 2003

Progressive muscle weakness in a 4 year old FS Coonhound
Contributed by Drs. Cathy Anderson and Jared Galle’
Animal Health Clinic, Fenton, MI (Anderson) and Oakland Veterinary Referral Service (Galle’)


Clinical History
 At approximately 6 months of age the dog was lethargic with episodic vomiting. A portosystemic (PSS) shunt or other hepatopathy was suspected based on the presence of  low serum albumin, total protein and BUN concentrations, markedly elevated fasting and post-feeding bile acid concentrations, and ammonium urate crystals in the urine. A portogram was performed that did not confirm the suspected shunt. The histological diagnosis was centrolobular hepatocellular degeneration with microvascular dysplasia suggestive of a PSS shunt. The dog was fed a low-protein diet which resulted in improved clinical signs and laboratory values. At 3 years of age the dog started showing signs of progressive exercise intolerance and weakness.

Physical Examination
On clinical presentation at 3 years of age, the dog appeared weak with a short-strided gait, exercise intolerance, and muscle tremors (See video clip). Spinal reflexes were assessed as normal initially, but patellar reflexes were absent on later evaluations. A neuromuscular disease affecting the neuromuscular junction or muscle was suspected.

Diagnostic Testing

Fasting bile acids – 265.7 mmol/l (reference 0-15.4)

Post-feeding bile acids – 297.2 mmol/l (reference 0-21.6)

Creatine kinase – 260 IU/L (reference 59-895)

Acetylcholine receptor antibody – 0.01 nmol/l (reference <0.6 nmol/l)

Urinary organic acid screen – Elevated malonic acid (44 mmol/mol creatinine; reference 0-1)


Muscle biopsy – In additional to non-specific myopathic changes, a prominent finding was the presence of central and subsarcolemmal PAS positive deposits within several muscle fibers. The deposits were at least partially diastase resistant.


A.


B.


C.

A. H&E stained paraffin section of the vastus lateralis muscle showing multiple vacuoles containing a greyesh blue substance.

B. PAS stained transverse muscle section demonstrating several myofibers containing PAS+ material (arrowheads). The PAS positive material was present in both central and subsarcolemmal distributions. The PAS positive deposits were partially diastase resistant (not shown).

C. PAS stained longitudinal muscle sections showing the central PAS+ deposits (dark reddish-purple) in muscle fibers.


Diagnosis
The PAS positive partially diastase resistant deposits within the muscle specimens are supportive of either a glycogen or polysaccharide storage disorder. While liver disease was diagnosed at an early age, histopathological evidence of inclusion material was not present. Further studies are in progress to more accurately define this disorder. Periodic updates will be given.

Comments
While we do not like to identify dogs or owners specifically by name, Izzy is a very special dog that is important to a very special girl named Gabe. Gabe also has a neurological disease and both have been featured on Animal Planet’s TV show “A Pet Story”. Repeats of the show featuring this very special girl and her very special dog will again air on February 17th, 2004 and February 18th, 2004 on Animal Planet TV. Please check your local listings for channel number and time. See website for up to date information www.gabeandizzy.com


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