Narcolepsy

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Sections available in full article Introduction, Presenting signs, Acute presentation, Geographic incidence, Age predisposition, Sex predisposition, Breed predisposition, Cost considerations, Special risks (e.g. anesthetic), Pathogenesis, Etiology, Predisposing factors, Pathophysiology, Timecourse (incubation, duration), Diagnosis, Clinical signs, Diagnostic investigation, Confirmation of diagnosis, Gross autopsy findings, Histopathology findings, Differential diagnosis, Treatment, Initial symptomatic treatment, Subsequent management, Prevention, Control, Sequelae, Prognosis, Expected response to treatment, Sources, Publications, Vetstream contributor(s),
Contributors Dr Masami Tonokura DVM
Dr Seiji Nishino MD PhD
Mr Simon Platt BVMS DipACVIM (Neurology) DipECVN MRCVS RCVS Specialist in Veterinary Neurology

Introduction

  • Chronic sleep disorder that affects dogs and humans.
  • Relatively rare; prevalence in dogs not known (human narcolepsy affects 0.02 to 0.18% of general population).
  • Human narcolepsy characterized by excessive daytime sleepiness, cataplexy (ie emotionally-elicited sudden loss of muscle tone that often leads to collapse) and other rapid eye movement (REM) sleep-related abnormalities (hypnagogic hallucinations and sleep paralysis).
  • In narcoleptic dogs most obvious symptom is cataplexy. Abnormal sleep tendency, not apparent.
  • In humans, laughing or anger often triggers cataplexy, while in dogs most typically elicited by presentation of food or by play. Dogs usually remain conscious during cataplexy, but cataplexy can be followed by sleep (unconsciousness), especially REM sleep.
  • Both familial (autosomal recessive) and sporadic cases observed.
  • Pathophysiology: abnormal transition to slow wave sleep and REM sleep, due to impaired hypocretin/orexin neurotransmission. Mutations in hypocretin receptor 2 in familial cases and loss of hypocretin/orexin peptides in sporadic cases.
  • Diagnosis: existence of cataplexy. Cataplexy is sudden onset of weakening of muscle tonus most typically elicited by emotional excitations. Attacks are often described as collapses, buckling of legs, drooping of neck, motionless immobility. Cataplexy needs to be differentiated from similar clinical signs eg epileptic seizures and syncope. No salivation, incontinence, spasm, cyanosis or dyspnea during cataplexy. Measurement of cerebrospinal fluid (CSF) hypocretin-1 levels useful for positive diagnosis in sporadic cases.
  • Treatment: anti-cataplectic medication.
  • Prognosis: neither progressive nor life threatening, but clinical signs persist throughout life. Narcoleptic dogs can be kept as pets with proper treatment and understanding of disease. If clinical symptoms are not manageable and quality of life is severely affected, owner may decide on euthanasia.

Diagnosis

Clinical signs

  • Cataplexy, most important symptom.
  • Symptoms of: daytime sleepiness, rapid eye movement (REM) related-sleep abnormalities not noticeable in dogs, except when exhibiting cataplectic attacks.
  • Triggered by excitation, most typically by feeding and playing.
  • Weakening of muscle tonus occurs in neck and limbs and dog often collapses.
  • Attacks last few seconds to several minutes.
  • During attacks, eyes are open and rapid eye movements, muscle twitching, repetitive movement of fore and hind limbs, may occur.
  • Attacks can be interrupted by various stimuli, such as calling dog's name or patting body.
  • Salivation and incontinence not observed during attacks.
  • No loss of consciousness. Dogs usually remain conscious with eyes open and are capable of following moving objects with eyes.
  • Familial cases: in young puppies, cataplectic attacks often appear as moments of behavioral arrest during nursing and suckling.
  • Sporadic cases: hypocretin ligand deficient narcoleptic dogs may be obese.

Diagnosis

Differential diagnosis

  • Cataplexy attacks must be differentiated from other episodic disturbances including syncope and seizures Seizures.
  • Heart disease.
  • Idiopathic Epilepsy: idiopathic or symptomatic epilepsy Epilepsy: traumatic.
  • Congenital malformations (hepatic-portal shunt Portosystemic shunt , hydrocephalus Hydrocephalus ).
  • Metabolic disease (hypoglycemia Hypoglycemia , hypocalcemia).
  • Inflammatory disease (granulomatous meningeal encephalitis Granulomatous meningoencephalomyelitis , distemper encephalitis Canine distemper disease ).
  • Toxins.
  • Metabolic storage disease Storage disease (GM2 gangliosides, ceroid lipofusinosis).
  • Neoplasia.
  • Trauma.
  • Neuromyopathy (myasthenia gravis Myasthenia gravis , multiple myositis Myositis ossificans ).

Sequelae

Prognosis

  • Good, if cataplexy not disabling and well controlled.
  • Neither progressive nor life-threatening.
  • Clinical signs persist throughout life.

Expected response to treatment

  • Reduction in cataplexy without side effects.
  • Complete suppression of cataplexy, rare.

Sources

Publications

Refereed papers

  • Recent references from PubMed.
  • Tonokura M, Fujita K & Nishino S (2007) Review of pathophysiology and clinical management of narcolepsy in dogs. Vet Rec 161 , 375-380 PubMed.
  • Tonokura M, Fujita K, Morozumi M, Yoshida Y, Kanbayashi T & Nishino S (2003) Narcolepsy in a hypocretin/orexin-deficient chihuahua. Vet Rec 152, 776-779. PubMed
  • Ripley B, Fujiki N, Okura M, Mignot E & Nishino S (2001) Hypocretin levels in sporadic and familial cases of canine narcolepsy. Neurobiol Dis 8, 525-534. PubMed
  • Nishino S, Riehl J, Hong J, Kwan M, Reid M & Mignot E (2000) Is narcolepsy a REM sleep disorder? Analysis of sleep abnormalities in narcoleptic Dobermans. Neurosci Res 38, 437-446. PubMed
  • Nishino S & Mignot E (1997) Pharmacological aspects of human and canine narcolepsy. Prog Neurobiol 52, 27-78. PubMed

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