ISSN 2398-2977      

CNS: narcolepsy / cataplexy

pequis

Synonym(s): Fainting disease


Introduction

  • Incurable, non-progressive pathologic condition of the CNS characterized by excessive sleepiness and cerebrocortical and voluntary muscle disassociation.
  • Cause: etiology unknown, deficiency in the quantity or signaling of the neuropeptide orexin (hypocretin).
  • Signs:
    • Narcolepsy: excessive daytime sleepiness and a pathologic manifestation of rapid eye movement (REM) sleep.
    • Cataplexy: periodic episodes of muscle weakness with full consciousness and sudden collapse.
  • Diagnosis: clinical signs and elimination of other neurologic and neuromuscular disorders.
  • Treatment: imiprimine hydrochloride (0.5-1.6 mg/kg PO BID) or amitriptylene (0.5 mg/kg PO BID).
  • Prognosis: non-progressive, proper treatment can minimize cataplexic episodes.

Pathogenesis

Etiology

  • Unknown, but thought to be pathologic manifestation of REM sleep, cerebrocortical and voluntary muscle disassociation. 
  • Recent research in people suggests that a deficiency or impaired signaling of the neuropeptide orexin (hypocretin) from a loss of orexin-producing neurons leads to episodes of daytime sleepiness.
  • Orexin-containing neurons are found in the posterior and lateral hypothalamus and project widely throughout the CNS, innervating aminergic and cholinergic regions that promote wakefulness. 
  • Low CSF concentrations of orexin have been found in human narcolepsy patients with cataplexy, whereas normal CSF concentrations of orexin were found in narcolepsy patients without cataplexy.

Predisposing factors

General
  • Normal behavior and physical examination findings between attacks. 
  • Attacks of acute weakness and recumbency may follow feeding, grooming, leading out of a stall, putting on tack or exercise.

Specific

  • Attacks may be precipitated by:
    • Grooming.
    • Stroking the head and neck.
    • Hosing or bathing after exercise.
    • Feeding (after first few mouthfuls of feed or water).
    • Leading the horse out of the stall.
    • Tacking-up and riding.
  • Episodes may occur daily or one every few months.

Timecourse

  • Normal behavior between episodes. 
  • Sudden onset of muscular weakness and collapse without prior warning.
  • Episodes may last from several minutes to 15-20 min.

Epidemiology

  • Sporadic outbreak in horses without other affected horses on a premises.

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.
  • Scammell T E (2003) The neurobiology, diagnosis, and treatment of Narcolepsy. Ann Neurol 53, 154-166 PubMed.
  • Ebrahim I O, Sharief M K, DeLacy S et al (2003) Hypocretin (orexin) deficiency in narcolepsy and primary hypersomnia. J Neruol Neurosurg Psychiatry 74 (1), 127-130 PubMed.
  • Peck K E, Hines M T, Mealey K L et al (2001) Pharmacokinetics of imipramine in narcoleptic horses. Am J Vet Res 62 (5), 783-786 PubMed.
  • Lunn D P, Cuddon P A, Saftoe S et al (1993) Familial occurrence of narcolepsy in Miniature Horses. Equine Vet J 25 (6), 483-487 PubMed.

Other sources of information

  • Andrews F M (1998) Seizures, narcolepsy, and cataplexy. In: Equine Internal Medicine. Eds: Reed S M & Bayly W M. W B Saunders Co, USA. pp 451-457.

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