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Cranial nerve disorders (Proceedings)

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Oct 01, 2008

1."Diseases" of CN III, IV, VI, and sympathetic to eye

a. Cavernous Sinus Syndrome

b. Idiopathic Horner's Syndrome

2. Trigeminal nerve diseases

a.Idiopathic Trigeminal Neuritis

b. Trigeminal nerve tumors

3. Facial nerve diseases

a. Idiopathic Facial Nerve Paralysis

b. Hemifacial Spasm

c. Neurogenic KCS

4. Vestibulo-cochlear nerve diseases

a. Idiopathic Vestibular Syndrome (Old dog vestibular syndrome)

b. Congenital Vestibular Syndrome

c. Bilateral Vestibular Syndrome

5. Diseases of Cranial Nerve IX and X

a. Laryngeal paralysis

b. Dysphagias

Cavernous Sinus Syndrome

The cavernous sinus is a venous structure that lies on the floor of the skull and encircles the pituitary. Disease in this area may result in abnormalities of CNs III, IV, VI, the ophthalamic branch of V, as well as sympathetic input to the eye. Causes: neoplasia and granulomatous disease.

Idiopathic Horner's Syndrome

Idiopathic postganglionic Horner's syndrome is seen most commonly in middle aged and older Golden Retrievers and Cocker Spaniels. The cause is unknown, but speculation exists for a viral or immune mediated (or both) etiology.

Clinical Signs: Miosis, enophthamus, and/or ptosis

Rule outs: Trauma, any lesion that can affect sympathetic pathway from hypothalamus to cervical cord to ventral neck, middle ear, and eye.

Diagnostics: Differentiating between preganglionic and postganglionic Horner's syndrome is best done 10 or more days after development of symptoms when the iris becomes super sensitive to sympathomimetics. Prepare a 1% solution of phenylephrine (take 5.0 mls of 2.5% phenylephrine (Mydfrin - Alcon) and add it to 7.5 mls of artificial tear to make a total volume of 12.5 mls) and apply one drop to each eye. If the Horner's pupil dilates to or near to the size of the control fellow eye in 20 minutes or less you have post-ganglionic Horner's. If it takes 40 minutes to get a response, or you do not get a response, then you likely have preganglionic Horner's.

Treatment: Most will improve without treatment in 6 to 16 weeks.

Prognosis: Depends on cause, but the signs themselves are not life threatening.

Idiopathic Trigeminal Neuritis (ITN)

Idiopathic Trigeminal Neuritis is characterized by the acute onset of inability to close mouth i.e. jaw paralysis, which results in difficulty eating or drinking and drooling. It occurs commonly in dogs and infrequently in cats, usually in middle to older aged animals. Pathologically, there is a nonsuppurative neuritis (demyelination and axonal loss) affecting primarily the mandibular branch (motor) of the trigeminal nerve. In one retrospective study of 29 dogs with ITN, golden retrievers were over-represented; age, sex, recent vaccination, or seasonal predispositions were not identified.

Clinical Signs: Sensory branches of trigeminal nerve were affected in 35 % of the cases. In that same study, 8 % of cases also had concurrent facial nerve deficits and 8 % had Horner's syndrome, suggesting that other cranial nerves may be affected. Neurogenic atrophy of the masticatory muscles may occur and can lead to trismus on some occasions.

Rule outs: Rabies, Encephalitis, Trauma

Diagnostics: Rule out other causes. In a retrospective study of cerebrospinal fluid (CSF) analysis in 9 dogs with ITN, 8 had abnormal results (mild to moderate elevations in total protein, nucleated cell count, or both). In 7 of these 9 dogs, needle electromyography (EMG) showed positive sharp waves, fibrillation potentials, or both in the masseter or temporalis muscles, confirming axonal injury to the trigeminal nerve.

Treatment: The condition may be immune-mediated but treatment with corticosteroids does not appear to enhance or shorten recovery. Assistance with eating and drinking is often necessary. Feed gruel-consistency dog food (dogs should still have the ability to lap liquids) or insert feeding tube (pharyngostomy, esophagostomy, PEG, etc).

Prognosis: The disease is usually self-limiting with recovery generally occurring in 1-9 weeks. Mean recovery time is about 3 weeks.