Neurologic and Musculoskeletal Conditions in Dogs (NAVLE Notes)
These neurologic and musculoskeletal disorders affect various dog breeds and can present with a range of symptoms. Here’s a concise overview for NAVLE preparation.
Fibrocartilaginous Embolism (FCE) / Type III Disc
- Classic Case:
- Signs: Acute, asymmetrical, non-painful, non-progressive para- or tetraparesis/plegia.
- Breeds: Often large non-chondrodystrophoid breeds; overrepresented in miniature schnauzers and Shetland sheepdogs.
- History: Typically follows vigorous exercise.
- Diagnosis:
- Imaging: MRI preferred; myelography may show normal or slight spinal cord swelling.
- Treatment:
- Bladder management if necessary (indwelling catheter or manual expression).
- Prevent decubital ulcers with frequent turning, well-padded bedding, and physical therapy.
- Steroids are controversial and generally avoided.
- Key Points:
- Initial onset may involve a yelp of pain, but FCE is typically non-painful.
- FCE involves embolization of fibrocartilage into the spinal cord, while a type III “missile” disc refers to acute non-compressive nucleus pulposus extrusion.
Otitis Media/Interna
- Classic Case:
- Signs: Head tilt (toward the lesion), horizontal nystagmus (fast phase away from the lesion), ataxia, and circling.
- Additional Signs: +/- Ipsilateral facial neuropathy, +/- ipsilateral Horner’s syndrome, no loss of conscious proprioception.
- Diagnosis:
- Imaging: MRI or CT; otoscopy; myringotomy with culture and sensitivity.
- Treatment:
- Myringotomy to aspirate fluid for cytology and culture.
- Antibiotics based on culture results.
- Bulla osteotomy if necessary.
- Key Points:
- Routes of infection include otitis externa, hematogenous spread, or via the auditory tube.
Encephalitis
- Classic Case:
- Signs: Vary based on the area(s) of the brain affected – seizures, circling, pacing, abnormal behavior, head pressing, adipsia, tetraparesis, head turn, hypermetria, head bobbing, ataxia, and neck pain.
- Diagnosis:
- CBC, CSF analysis, cytology, culture, and sensitivity.
- Infectious disease titers or PCR (distemper, Toxoplasma, Neospora, Cryptococcus, Ehrlichia canis, Rickettsia rickettsia).
- MRI if available.
- Treatment:
- Depends on etiology:
- Idiopathic: Immunosuppression.
- Fungal: Antifungals.
- Rickettsial: Doxycycline.
- Bacterial: Antibiotics.
- Protozoal: Clindamycin or sulfonamides.
- Viral: Supportive care.
- Key Points:
- Some breeds (e.g., pugs, Maltese) are predisposed to breed-related encephalitis, such as necrotizing meningoencephalitis.
- Granulomatous meningoencephalomyelitis (GME) is the most common noninfectious cause.
- Rabies should always be considered.
Idiopathic Laryngeal Paralysis
- Classic Case:
- Signs: Stridor, dysphonia, retching or coughing when eating or drinking.
- Breeds: Older large or giant breeds, particularly Labrador Retrievers, Chesapeake Bay Retrievers, Irish Setters, Afghan Hounds, St. Bernards, Rottweilers.
- Diagnosis:
- Laryngoscopy under light anesthesia.
- Rule out hypothyroidism and myasthenia gravis.
- +/- Electromyography.
- Treatment:
- Exercise restriction, stress avoidance, avoid obesity.
- Arytenoid lateralization (tie-back surgery) if severe.
- Key Points:
- Prognosis is guarded to good if managed appropriately.
- Surgical complications include aspiration pneumonia, coughing, gagging, and exercise intolerance.
Acquired Myasthenia Gravis
- Classic Case:
- Signs: Episodic weakness, worsens with exercise; coughing, gagging, regurgitation; palpebral reflex may be absent with repeated stimulation.
- Breeds: German Shepherds and Golden Retrievers have high morbidity.
- Diagnosis:
- Acetylcholine receptor antibody test (gold standard).
- Edrophonium (Tensilon®) challenge test (keep atropine on hand for potential cholinergic crisis).
- Thoracic radiographs to assess for megaesophagus, aspiration pneumonia, or thymoma.
- Treatment:
- Supportive care and antibiotics for aspiration pneumonia.
- Elevated feeding to prevent aspiration.
- Anticholinesterase drugs (e.g., pyridostigmine).
- Immunosuppression is controversial due to high aspiration pneumonia risk, though mycophenolate mofetil may be used.
- Key Points:
- Prognosis is guarded with concurrent megaesophagus and aspiration pneumonia.
NAVLE-Style Practice Questions on Neurologic and Musculoskeletal Conditions
Question 1
A 5-year-old Miniature Schnauzer presents with acute onset of non-painful, asymmetrical paraparesis following vigorous exercise. MRI shows minor swelling of the spinal cord, but no compressive lesions are observed. What is the most likely diagnosis?
- A) Intervertebral disc disease
- B) Fibrocartilaginous embolism (FCE)
- C) Encephalitis
- D) Idiopathic laryngeal paralysis
Correct Answer: B
Explanation: FCE commonly presents as an acute, non-painful onset of paraparesis after exercise, especially in breeds like Miniature Schnauzers. MRI findings align with FCE, which does not involve compressive lesions.
Question 2
An 8-year-old Labrador Retriever is brought in for noisy breathing, dysphonia, and frequent coughing during meals. Physical exam reveals exercise intolerance. What is the most likely diagnosis, and what is the initial step in diagnosis?
- A) Encephalitis; perform a CBC and CSF analysis
- B) Idiopathic laryngeal paralysis; perform laryngoscopy under light anesthesia
- C) Otitis media/interna; perform otoscopy
- D) Acquired myasthenia gravis; order acetylcholine receptor antibody test
Correct Answer: B
Explanation: The signs are consistent with idiopathic laryngeal paralysis, commonly seen in older large breed dogs. Laryngoscopy under light anesthesia is the preferred diagnostic approach to confirm paralysis of the arytenoid cartilages.
Question 3
A 3-year-old German Shepherd presents with intermittent regurgitation, episodic weakness that worsens with exercise, and absent palpebral reflex on repeated testing. What is the most appropriate diagnostic test?
- A) MRI to assess brainstem function
- B) Acetylcholine receptor antibody test
- C) Edrophonium challenge test
- D) Electromyography
Correct Answer: B
Explanation: The episodic weakness, regurgitation, and absent palpebral reflex are suggestive of myasthenia gravis, which can be confirmed with an acetylcholine receptor antibody test.
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