Neurology Case of the Month (June 2013): Chesapeake Bay Retriever with difficulty chewingWritten on June 18, 2013 by Mark Troxel, DVM, DACVIM (Neurology) Hospital: Massachusetts Veterinary Referral Hospital

Signalment: 6 yr FS Chesapeake Bay Retriever

History: The patient was presented for evaluation of a 3-day history of difficulty eating and being a sloppy eater.

 

Case Video:

Physical Exam: No significant abnormalities

NEUROLOGICAL EXAM

Mental status: BAR
Gait/posture: Normal gait/posture
Cranial nerves: Dropped jaw, unable to physically close the jaw, remainder WNL
Postural reactions:
Normal CP/hop x 4
Spinal reflexes: WNL x 4
Withdrawal: WNL x 4
Spinal pain: None
Muscle tone: Normal x 4
Muscle atrophy: None
Pain sensation: Normal x 4
Cutaneous trunci: WNL bilaterally

 

What is your neuroanatomic localization?
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Neurolocalization: Bilateral mandibular branch of trigeminal nerves (cranial nerve V)

 

What are the differential diagnoses and what is the primary differential diagnosis for this patient? How do you treat this condition?

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Differential diagnoses:

  • Idiopathic Trigeminal Neuritis – Most common cause of dropped jaw
  • Trauma
  • Rabies
  • Hypothyroidism
  • TMJ disease
  • Lymphosarcoma
  • Neoplasia of CN V
  • Neospora caninum
  • Rickettsial vasculitis
  • Idiopathic polyneuritis

Diagnostics
The patient was current on all vaccines, including rabies. A CBC, biochemical profile and total T4 were performed to rule out other possible metabolic/systemic causes of dropped jaw. The results were within normal limits.

Presumptive diagnosis: Idiopathic Trigeminal Neuritis

Treatment
Supportive care with small frequent feedings with a gruel consistency to allow the dog to lap up the food. Some people suggest a tape muzzle to keep the mouth partially closed allowing the dog to eat better, but this is rare needed in my experience. In rare cases, a feeding tube may need to be placed to ensure adequate nutrition. However, most dogs are able to lap up enough food to maintain adequate nutrition. No medications, including corticosteroids, have been proven to speed or improve recovery.

Prognosis & Outcome
The prognosis for Idiopathic Trigeminal Neuritis is very good to excellent with supportive care and time. The patient made a full recovery in 3-4 weeks.

NOTES:
Idiopathic Trigeminal Neuritis has no known cause; some speculate an immune-mediated cause, but corticosteroids have not been shown to shorten or improve recovery. Histologically, there is a nonsuppurative neuritis characterized by demyelination and axonal loss. It usually affects primarily the mandibular (motor) branches of the trigeminal nerve which leads to a dropped jaw (inability to close the mouth) with secondary drooling (unable to keep saliva in mouth to swallow) and sloppy eating/drinking. The patients are often noted to lap their food only. In one study, 35% of patients also had sensory deficits, 8% had facial nerve paresis/paralysis, and 8% had Horner’s Syndrome. There is no antemortem test that will definitively diagnose the condition. The minimum database includes CBC, biochemical profile, and total T4. Advanced diagnostics (see below) can help rule out other causes for dropped jaw. IMPORTANT: You should always verify a current rabies vaccine status since rabies can cause a dropped jaw and drooling. If you are unable to verify rabies vaccine status, be sure to wear exam gloves and limit interaction with personnel until the patient’s status is obtained.

Advanced diagnostics

  • MRI may show enlarged trigeminal nerves with contrast enhancement
  • CSF may show mild elevated total protein level and/or total nucleated cell count
  • Electrodiagnostics often show abnormal spontaneous muscle activity

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