Clinical History
A 4-year-old male Cocker Spaniel presented for dysphagia, retching and coughing of 5 days duration, which was notably worse after eating. Exercise intolerance was not described.  Hematology and serum biochemistry performed in-house prior to referral was considered to be normal. Additionally, endoscopic examination of the upper respiratory and gastrointestinal tracts was unremarkable. There was progression of the clinical signs to include excessive drooling with notable bilateral muscle atrophy of the muscles of the head.

Physical and Neurological Examination
The dog was generally well-muscled apart from decreased muscle mass over the cranium (see figure).  Increased jaw tone was noted with severely restricted jaw movement. Prehension of food or water was not possible. Excessive drooling was exhibited from both sides of the mouth, and bilateral mild ventrolateral strabismus was noted. A focal myopathy suggestive of masticatory muscle myositis (MMM) was suspected.

Diagnostic Testing

CBC – No significant abnormalities.
Serum chemistry profile – CK 489 IU/L (reference range 21-56 IU/L).
Toxoplasma and Neospora serology – Negative.
PCR analysis for canine Distemper virus, Toxoplasma gondii and Neospora caninum infections – Negative.
Thoracic radiographs (3 views) – Within normal limits.                                             
Electrophysiology – No abnormalities detected on needle electromyography of the cranial and appendicular muscles, motor nerve conduction velocity of the thoracic and pelvic limbs, and repetitive stimulation examinations.
Cisternal cerebrospinal fluid analysis – Within normal limits.
Muscle biopsy of the temporalis and lateral head of the triceps – Within normal limits.
Serum antibodies against masticatory muscle type 2M fiber proteins - Negative

Diagnosis and Treatment
Diagnostic testing did not provide evidence for an underlying myopathy and no specific therapy was instituted. Supportive care included the placement of a PEG tube and tracheostomy tube. A cranial magnetic resonance imaging study was considered to rule out a central nervous system disorder. However, over the next 48 hours the clinical signs progressed to include a stiff gait, exacerbated by activity and stress (Go to video clip). Tetanus was suspected and therapy was initiated with a combination of metronidazole 15 mg/kg q 12hrs IV, benzylpenacillin 10 mg/kg q 8hrs IV and diazepam 0.5 mg/kg q 8hrs via the PEG tube. The owner was questioned repeatedly about the possibility of prior skin wounds. The owner did recount noting a small laceration of the tongue after a walk in a woodland approximately 3 weeks before. There was significant improvement in the dog’s clinical status over the next 7 days. The tracheostomy tube was removed at this time and the dog was discharged, with instructions for PEG tube management. Continued improvement to normality was noted over the next month when the PEG tube was removed.

Clinical Course and Outcome
Although initially suspected to be MMM, this case represented an unusual presentation of suspected tetanus. The response to therapy for tetanus supports this diagnosis. A complete diagnostic evaluation was necessary to rule out MMM and avoid unnecessary immunosuppressive therapy with prednisone.