Comparative Neuromuscular Laboratory

NEUROMUSCULAR CASE OF THE MONTH - JULY 1999

Acute onset of megaesophagus in a
4 year old male castrated English Setter
Contributed by Dr. Sara Ford
VCA Emergency Animal Hospital & Referral Center
San Diego, CA

Clinical History
The owner reported a recent onset of cough followed by regurgitation. No other problems were present historically. With the exception of a monthly flea preventative, the dog was not on any medications.

Physical Examination
General physical examination showed the dog was coughing and tachypneic with bilateral inspiratory crackles on thoracic ascultation. No abnormalities were observed on cranial nerve examination or evaluation of spinal reflexes. Neither muscle weakness or atrophy was present.

Diagnostic Tests
Routine laboratory tests
    CBC - eosinophilia (9504/ul; reference 0-1200)
    CK - 171 IU/L (59-895)
    Electrolytes - normal
    Heartworm test - negative
    Fecal flotation and Baermann test - negative

Thoracic radiographs - Esophageal dilation was obvious on a lateral radiograph of the chest (Fig. 1). The solid arrows delineate the ventral border of the dilated esophagus. Also present was a solitary pulmonary nodule (open arrow).

Thyroid panel
    Total thyroxine (TT4) - 17 (15-50 nmol/L)
    Total triiodothyronine (TT3) - 0.9 (1.0-2.5 nmol/L)
    Free T4 - 12 (12-33 pmol/L)
    Free T3 - 2.7 (2.8-6.5 pmol/L)
    T4 autoantibody - 7 (<20)
    T3 autoantibody - 4 (<10)
    Thyroid stimulating hormone - 32 (0-30 mU/L)
    Thyroglobulin autoantibody - 50 (<200)

Serum AChR antibody titer - 0.02 (<0.6 nmol/l)

ACTH stimulation - Pre 1.6 (1.0-5.0 ug/dl); Post 11.8 (8-17 ug/dl)

Serum antinuclear antibody - Negative at 1:20

Tick titers negative for antibodies to E. canis, B. canis, R. rickettsii, B. burgdorferi

Barium swallow - Decreased primary and secondary esophageal peristaltic waves with mild dysphagia

Cytology of aspirate from pulmonary nodule - Inflammation with many eosinophils

Aspirate smears of lungs not associated with nodule - Marked increase in the number of eosinophils/number of red blood cells.

Bronchoalveolar lavage - Benign respiratory epithelial cells and numerous eosinophils

Esophagoscopy with flexible fiberoptic endoscope - No evidence of esophageal reflux

Muscle biopsy - A biopsy from the vastus lateralis muscle showed multifocal areas of cellular infiltration composed predominantly of eosinophils (Figure 2. ). The eosinophils were highlighted by the peroxidase reaction and stain a gold-brown color.

Figure 1.

Figure 2.

Treatment
Intravenous dexamethasone sodium phosphate (0.25 mg/kg) was given post bronchoscopy followed by subcutaneous injections of prednisone acetate (1 mg/kg BID). A PEG tube was placed for facilitation of feeding and medications including Carafate. Other treatments included Timentin and Baytril for an aspiration pneumonia, Zantac for reflux esophagitis, and Terbutaline for bronchodilatation. Repeat thoracic radiographs 14 days later showed resolution of the megaesophagus. Eosinophilia was no longer present on repeat CBC. Based on results of an allegery test panel, hypersentization treatments were initiated.

Conclusion and Comments
A diagnosis of hypereosinophilic syndrome including pulmonary infiltrates with eosinophilia (PIE) and eosinophilic myositis was determined based on the demonstration of eosinophils within aspirates of a solitary pulmonary nodule, bronchoalveolar lavage and aspirate smears of lung containing eosinophils, circulating eosinophilia, and localization of eosinophilic infiltrates within a limb muscle biopsy. A reversible megaesophagus was also present. Since the canine esophagus is composed predominantly of skeletal muscle, disorders that affect limb muscle may also affect the esophageal musculature. Differentials for acquired megaesophagus include myasthenia gravis, hypoadrenocorticism, polymyositis, polyneuropathy, hypothyroidism (?), and idiopathic causes. For optimal treatment of acquired megaesophagus and a favorable clinical outcome, early recognition and identification of the underlying etiology, if possible, is important. In this case, polymyositis was associated with an eosinophilic syndrome. Esophageal dilatation was resolved within 14 days of treatment with prednisone. Since PIE may be associated with allergy, and this dog was found to be sensitive to numerous antigens on allergy testing, densensitization treatment was initiated.. The dog continues to be symptom free 3 months after clinical diagnosis.