Overview
Narcolepsy/cataplexy refer to the same disorder, cataplexy being the clinical sign easiest to recognize in domestic animals.
Narcolepsy
- Sleep disorders.
- Syndrome characterized by excessive sleepiness, cataplexy sleep paralysis, and hypnagogic hallucinations (humans). Sudden episodes of paradoxical sleep without a preceding period of slow-wave sleep.
Cataplexy
- Sudden, episodic, and spontaneous collapse secondary to complete atonia of skeletal muscles (flaccid paralysis) caused by inhibition of spinal cord lower motor neurons.
- Patient stays alert and will follow with its eyes.
- Most common clinical sign of narcolepsy in small animals.
Signalment
- Dog and rarely cat.
- Proven hereditary-Labrador retriever, dachshund, and Doberman pinscher.
- Autosomal recessive gene mutation-canarc-1 gene found on chromosome 12, which codes for a hypocretin (orexin) receptor. Mutations of OxR2 (type II orexin receptor gene). Increased microglial expression of MHC II in Doberman pinscher.
- Assumed genetic basis for miniature poodle-mode of inheritance unknown.
- For inherited disease, clinical signs appear between 2 and 4 months of age with escalation of signs around 1 year of age. Possible disappearance of clinical signs later in life.
- Acquired form may develop in older animals (possible depletion of hypocretin production by hypothalamus) and can occur in any dog breed or mixed breed, at any age.
- Clinical signs in acquired form will usually remain for life.
Signs
- Physical and neurologic examinations-normal except during an episode.
- Onset-peracute.
- Excessive daytime sleepiness and fragmented sleep patterns reported in domestic animals, but cataplexy is usually the clinical sign recognized by owners.
- Cataplexy episodes-acute onset of flaccid paralysis without loss of consciousness lasting a few seconds to minutes (up to 20 minutes) with sudden return to normal; multiple episodes in 1 day.
- Narcolepsy-eye movements, muscular twitching, and whining (as in REM sleep) frequently observed during episodes.
- Patients are usually aroused by loud noises, petting, or other external stimuli.
Causes & Risk Factors
- Hereditary in some breeds.
- Possible immune system involvement in acquired disease.
- Neurotransmitter abnormalities-serotonin, dopamine, norepinephrine, neuropeptide hypocretin (orexin).
- Rarely reported with pontomedullary (brainstem) lesions.
- Excitement, emotions, feeding, and general anesthesia may induce narcoleptic episodes.
