ISSN 2398-2969      

Trigeminal neuropathies

icanis

Synonym(s): Trigeminal neuritis, Idiopathic trigeminal neuropathy, Mandibular nerve neurapraxia, Idiopathic mandibular paralysis


Introduction

  • Trigeminal nerve branches: ophthalmic, maxillary, mandibular.
  • Most common trigeminal neuropathy is idiopathic mandibular paralysis.
  • Cause: inflammation, neoplasia, trauma.
  • Signs:
    • Ophthalmic branch: corneal anesthesia, loss of sensation to nasal septal mucosa, skin on dorsum of nose, upper eyelid, eye medial canthus.
    • Maxillary branch: loss of sensation to eye lateral canthus, lower eyelid, skin of the cheek, side of the nose, muzzle, palates, mucous membrane of nasopharynx, teeth and gingiva of upper jaw.
    • Mandibular branch: unilateral or bilateral paralysis of masticatory muscles → inability to close mouth, difficulty eating and drinking. Loss of sensation to mandibular portion of the face and oral cavity.
  • Diagnosis: signs, histopathology, MRI.
  • Treatment: supportive care.

Pathogenesis

Etiology

  • Idiopathic.
  • Space-occupying lesions, eg neoplasia.
  • Trauma to head, especially jaw.
  • Trigeminal nerve abnormalities can occur with infiltrating neoplasia (lymphosarcoma, leukemias Leukemia ), that involve a branch or the entire nerve.
  • Other cranial nerves (VII), and the sympathetic supply to the eye may be involved concurrently.
  • Animals that have systemic hematological neoplasia that develop cranial nerve abnormalities should be evaluated for extension of the tumor to these sites.
  • Nerve sheath tumors Nerve sheath: neoplasia may arise within the trigeminal nerve:
    • Clinical signs of unilateral temporalis and masseter muscle ipsilateral to the lesion are most common.
    • The lesion is found with CT and, more often, MR imaging.
    • Surgical treatment can result in long-term resolution of the disease.
  • Trigeminal neuritis is an idiopathic inflammatory disease of the mandibular branches of V bilaterally:
    • The dog presents with a dropped jaw.
    • The etiology is unknown.
    • A non-suppurative inflammatory neuritis in the motor branches of the trigeminal nerve and its ganglion has been confirmed in some cases.
    • Most dogs should improve with time (within 2-10 weeks).
    • No treatment has shown benefit.

Pathophysiology

  • Inflammation or degeneration trigeminal nerve → loss of trigeminal nerve function → loss of sensation to face and mouth, loss of motor function to masticatory muscles → unable to close jaw → masticatory muscle atrophy.
  • A unilateral dysfunction of all three branches of V is almost always associated with a peripheral V lesion (outside the brain stem), because the nuclear areas of V are so extensive that central destruction of all of these nuclei would be incompatible with life.
    Remember, just because a lesion is peripheral it does not mean that it is not intracranial, eg a tumor involving CN V in the trigeminal canal.

Diagnosis

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Treatment

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Milodowski E J, Amengual-Batle P, Beltran E et al (2019) Clinical findings and outcome of dogs with unilateral masticatory muscle atrophyJ Vet Intern Med 33, 735-742 PubMed.
  • Kent M, Glass E N, de Lahunta A et al (2013) Prevalence of effusion in the tympanic cavity in dogs with dysfunction of the trigeminal nerve: 18 cases (2004-2013).  J Vet Intern Med 27, 1153-1158 PubMed.
  • Roynard P, Behr S, Barone G et al (2012) Idiopathic hypertrophic pachymeningitis in six dogs: MRI, CSF and histological findings, treatment and outcome. J Small Anim Pract 53, 543-548 PubMed.
  • Mayhew P D, Bush W W, Glass E N (2002) Trigeminal neuropathy in dogs: a retrospective study of 29 cases (1991-2000).  J Am Anim Hosp Assoc 28, 262-270 PubMed.
  • Pfaff A M, March P A, Fishman C (2000) Acute bilateral trigeminal neuropathy associated with nervous system lymphosarcoma in a dogJ Am Anim Hosp Assoc 36, 57-61 PubMed.
  • Bagley R S, Wheeler S J, Klopp L et al (1998) Clinical features of trigeminal nerve sheath tumor in 10 dogs. JAAHA 34 (1), 19-25 PubMed.
  • Carpenter J L, King Jr N W & Abrams K L (1987) Bilateral trigeminal nerve paralysis and Horner's syndrome associated with myelomonocytic neoplasia in a dog. JAVMA 191 (12), 1594-6 PubMed.
  • Christopher M M, Metz A L, Klausner J et al (1986) Acute myelomonocytic leukemia with neurologic manifestations in the dog. Vet Pathol 23 (2), 140-7 PubMed.

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