Canis ISSN: 2398-2942

Facial nerve neuropathies

Synonym(s): Facial nerve neuritides

Contributor(s): Paul Cuddon, Laurent Garosi

Introduction

  • Intermittent facial spasms or uni- or bilateral facial paralysis or paresis.
  • Cause: can be immune mediated, or due to inflammation, eg otitis media/interna, infection, myasthenia gravis, toxins, eg botulism, trauma, neoplasia, (both extracranial and intracranial), toxic (hypersensitivity associated with potentiated sulfonamides), idiopathic, <75% of cases in 1 study.
  • Also seen in conjunction with polyradiculoneuropathy, polyneuropathy, and hypothyroidism.
  • Signs: drooping and inability to move the ear and lip, drooling, widened palpebral fissure, absent abduction of nostril during inspiration, deviation of nose towards normal side, absent spontaneous or provoked blinking.
  • Diagnosis: signs, EMG, nerve conduction studies, brainstem auditory evoked responses (BAER), MRI, CT scan, autoscopic examination.
  • Treatment: symptomatic for the facial nerve paralysis, specific treatment for the primary disease may reverse the facial neuropathy.
  • Prognosis: guarded for the complete return of function.

Pathogenesis

Etiology

Idiopathic facial paralysis
  • Active degeneration of large and small caliber myelinated nerve fibers without inflammation.
  • The inciting cause is unknown.
  • Most common cause in dogs (75%).
  • Appears analogous to Bell's Palsy in humans.

Facial paralysis

Predisposing factors

General
  • Head/face trauma.

Specific

  • Hypothyroidism.

Pathophysiology

  • Degeneration of facial nerve.
  • The facial canal that is adjacent to the tympanic cavity lacks a bony wall for a very short distance as it runs in the petrosal portion of the temporal bone. This leaves the facial nerve exposed to the cavity and therefore to disease processes affecting the middle ear.
  • Otitis media/interna → damage to facial nerve as it passes between middle and inner ear → loss of function → unilateral paralysis of facial muscles or hemifacial spasm.
  • Other causes of damage to facial nerve anywhere along its course → axonal damage especially of large-diameter myelinated fibers → loss of function of facial muscles or facial spasm.
  • A primary irritation of the facial nerve nucleus or increased excitability of the facial nucleus by upper motor neuron dysfunction can also cause hemifacial spasm.

Timecourse

  • Most times onset of facial neuropathy is acute.
  • Most cases have severe paresis and paralysis of the facial nerve which remains static.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Garosi LS, Lowrie M L & Swinborune N F (2012) Neurologic manifestation of ear disease in dogs and cats. Vet Clin North Am Small Anim Pract 42, 1143-1160 PubMed.
  • Smith P M et al (2012) Sensitivity and specificity of MRI for detecting facial nerve abnormalities in dogs with facial neuropathy. Vet Rec 171, 349 PubMed.
  • Van Meervenne S A et al (2008) Hemifacial spasm associated with an intracranial mass in two dogs. JSAP 48, 472-475 PubMed.
  • Varejao A S, Munoz A, Lorenzo V (2006) Magnetic resonance imaging of the intratemporal facial nerve in idiopathic facial paralysis in the dog. Vet Radiol Ultrasound 47, 328-333 PubMed.
  • Garosi L S et al (2003) Review of diagnostic imaing of ear diseases in the dog and cat. Vet Radiol Ultrasound 44, 137-146 PubMed.
  • Trepanier L et al (2003) Clinical findings in 40 dogs with hypersensitivity associated with potentiated sulfonamides. JVIM 17, 647-652 PubMed.
  • Braund K G et al (1987) Insulinoma and subclinical peripheral neuropathy in two dogs. J Vet Intern Med (2), 86-90 PubMed.
  • Kern T J et al (1987) Facial neuropathy in dogs and cats - 95 cases (1975-1985). JAVMA 191 (12), 1604-1609 PubMed.

Other sources of information

  • Summers B Aet al(1995)Idiopathic facial nerve paralysis in the dog and cat.In:Veterinary Neuropathy.St Louis: Mosby Year Book. pp 448.


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