NEUROMUSCULAR CASE OF THE MONTH - MAY 2000

Polymyositis and megaesophagus in a
5 year old neutered male Basset hound
Contributed by David A. Serra, VMD
Wood River Animal Hospital
28 Kingston Road
Wyoming, RI 02898


Clinical History
A 5.5 year old neutered male Basset hound presented to the Wood River Animal Hospital with a 2 week history of regurgitation of food within 1 hour of eating. He would regurgitate white foamy mucus overnight. He had lost 20% of his body weight during this 2 week period. Abdominal and thoracic ultrasound examinations were normal the day prior to referral.

Physical Examination
The dog was depressed and trembling. He was judged to be 5% dehydrated. There was mild popliteal lymphadenopathy and palpable foam and air bubbles in the cervical portion of the esophagus. The remainder of the physical examination was normal. The dog's depressed mental and physical state made evaluation of the neuromuscular system difficult, but it was judged to be normal with the exception of pain on palpation of the triceps, biceps and quadriceps muscles. Although he was weak, his neurological examination was also judged to be normal. Fatigability was difficult to assess, but the palpebral reflex was not fatigued after repeated stimulation.

Radiographic Evaluation
Thoracic radiographs showed an air-filled caudal esophagus. A barium swallow further defined a dilated, hypomotile esophagus consistent with a diagnosis of megaesophagus (Fig. 1). Barium filled the esophagus for 24 hours after administration of the contrast agent (Fig. 2).
Figure 1.


Figure 2.

Diagnostic Tests
CBC and biochemical analysis:
   
WBC 30.6 (reference 6.0-17.0 x103/µl)
     Polys 24480 (reference 3500-14500/µl)
     Bands 1224 (reference 0-300/µl)
     Eos 1836    (reference 0-1500/µl)
 Serum creatine kinase (CK) - 1782 (reference 10-150 U/L)
Thyroid Profile
  
      cTSH    0.48 (reference 0.02-0.60 ng/ml)
      FT4       23 (reference 11-43 pmol/L)
Thyroglobulin autoantibody -  Neg  
Acetylcholine receptor antibody titer - 0.05 (reference <0.6 nmol/l)


Assessment
Based on the elevated CK concentration, a presumptive diagnosis of an inflammatory myopathy was made. There were still questions as to whether this represented a generalized condition (polymyositis) or a focal inflammatory myopathy and if an etiology could be identified. Biopsies were taken from the biceps brachii and vastus lateralis muscles. A PEG tube was placed at the time of muscle biopsy to accomplish nutritional support for the patient at home.

Muscle Biopsy
Fresh frozen biopsies from the biceps brachii and vastus lateralis muscles showed multifocal areas of mononuclear cell infiltration composed of lymphocytes and scattered macrophages (Fig. 3). The cellular infiltrates had an endomysial distribution with invasion of non-necrotic fibers. No organisms were observed. Using the peroxidase reaction, several eosinophils were highlighted (dark brown staining) within the perimysial and endomysial connective tissue (Fig. 4). The biopsy findings confirmed the presence of an inflammatory myopathy.



Figure 3. H&E stain of the
vastus lateralis muscle biopsy


Figure 4. Peroxidase reaction for the localization of eosinophils
(dark brown stain)

Radiographic Evaluation
Additional testing was performed in an attempt to determine a precise etiology of the inflammatory myopathy. A serum antinuclear antibody titer was negative, as was a blood lead level, IgG and IgM antibodies for Toxoplasma gondii, and Lyme disease (IgG). No evidence of neoplasia was found. While awaiting results of the muscle biopsy, the dog was sent home on frequent feedings of a highly digestible, low residue canned food (Hills Prescription Diet i/d) in a quantity to meet maintenance plus surgical stress requirements. Over the next 10 days the dogs condition improved dramatically. By 3 weeks post PEG tube placement he was tolerating oral feeding without regurgitation. A barium swallow was normal one-month post presentation. The plan was to continue on no therapy for one month and then recheck the CK and barium swallow. Within 2 weeks he presented for regurgitation and a repeat barium swallow confirmed esophageal hypomotility, although barium reached the stomach within 10-15 minutes vs 24 hours initially. The serum CK was 375 U/L  immunosuppressive therapy with azathioprine was begun at 2 mg/kg body weight once daily. A CBC was rechecked every 10 days for the first month then every 2 weeks the second month. One month later, the barium swallow showed marked improvement of esophageal function and resolution of the megaesophagus (Fig. 5). The serum CK was 133 U/L. The PEG tube(Fig. 6) was replaced with a low profile stomate tube (Flexiflo Stomate gastrostomy tube, Ross laboratories, Columbus, OH 43216) for long-term access if needed. The dog remained on azathioprine for 6 months then it was discontinued. The megaesophagus has not returned during a 2-year follow-up period.

 


Figure 5. Megaesophagus
was no longer apparent at
one month following initiation
of azathioprine therapy



Figure 6. A PEG tube was
placed for nutrition and
hydration


Discussion
Management of esophageal disease has been enhanced and uncomplicated by the advent of the PEG tube, particularly when replaced by low profile tubes. This dog tolerated the presence of the tube for two years without complication. The author has managed dogs for up to four years with similar favorable results. The ease of providing nutritional support by this method will certainly help change the management of esophageal dysfunction in the future. This dog is also another example of  a reversible megaesophagus most likely associated with a generalized skeletal muscle disorder. While a precise cause of the polymyositis could not be determined, the most likely etiologies would included immune-mediated or infectious disorders. Neoplasia was not detected at the time of diagnosis or after a two year follow-up. The dog was treated for Dirofilariasis two years after resolution of his myopathy but he had two negative occult heartworm antigen tests in the intervening time period.

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