NEUROMUSCULAR CASE OF THE MONTH - AUGUST 2000

Myopathy associated with megaesophagus in a 1 year old castrated male Springer Spaniel
Contributed by Dr. Melissa Moore
Muddy Creek Animal Care Center
Rowley, MA 01969

Clinical History At approximately 5 months of age, the dog began having problems with intermittent "vomiting". Another veterinarian was treating the dog with unspecified therapies over the next 9 months with no specific diagnostics performed. A second opinion was sought and it was thought that the history was more compatible with regurgitation than vomiting. The owner also reported that the dog was having problems jumping into the car and onto the bed. Physical Examination Atrophy was noted (Figs. 1,2) of the temporalis, semimembranosis, semitendinosis, and triceps muscles with the temporalis muscle most markedly affected. No abnormalities of jaw movement or jaw pain were observed.  No other specific abnormalities were found on the physical or neurological examinations.

Figure 1. Note atrophy of the temporalis muscle Figure 2. Atrophy of selected limb muscles was also present

Muscle Biopsy Fresh and fixed specimens were collected from the temporalis, triceps, and vastus lateralis muscles. Similar pathological abnormalities were observed within all three muscles. There was variability in myofiber size with round atrophy involving both fiber types. Several muscle fibers within each biopsy contained central, well demarcated areas of basophilia (H&E; Fig. 3). These central areas were highlighted by the stains for oxidative enzymes including succinic dehydrogenase (SDH) and cytochrome C oxidase (COX; Fig. 4). A marked type 1 fiber predominance was present. The central accumulations were present within type 1 fibers (not shown).

Figure 3. H&E stain of vastus lateralis muscle biopsy Figure 4. Cytochrome C oxidase reaction showing dark staining central areas

Conclusion
The pathological changes within the muscle biopsies are consistent with a congenital non-inflammatory myopathy and are similar to those previously reported in so-called "Central core myopathy" in Great Danes (J Small Animal Prac 1994:35; 100-103, and Shelton unpublished). These structures differ from a similarly named myopathy in humans. Staining for SDH and COX localization was strong, suggesting that the central structures may be accumulations of mitochondria. Based on this assumption the dog was treated with a combination of L-carnitine (50 mg/kg BID) and coenzyme Q10 (100 mg daily). The owners report improvement in muscle strength and markedly decreased frequency of regurgitation, although the megaesophagus is still radiographically present 10 months following diagnosis and initiation of therapy.

UPDATE: Bailey was euthanized in September 2003 due to progression of his muscle disease. He was having extreme difficulty swallowing and regurgitating most of the food he consumed resulting in significant weight loss. The owners were kind enough to allow the evaluation of further muscle specimens following euthanasia. As shown below, core like structures filled most of the myofibers in limb muscle (A) and were also present within the esophageal musculature (Fig. B is at low power and Fig. C is at higher power. Arrows indicate core-like structures). Since muscle in the canine esophagus is predominantly striated, pathological changes that affect limb muscle also affect the esophageal musculature.

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