Cataplexy

Clinic

• Cataplexy is a sudden and transient episode of muscle weakness accompanied by full conscious awareness
• It is typically triggered by emotions such as laughing, crying, or terror.
• Orexin regulates arousal and has a role in stabilization of the transition between wake and sleep states.

• He remains conscious throughout the episode.
• Cataplexy may resemble epileptic seizures.
• Cataplexy can cause extreme anxiety, fear, and avoidance of people or situations that might elicit an attack.
• Cataplexy is generally considered to be unique to narcolepsy

Cataplexy vs RBD

• Cataplexy is analogous to sleep paralysis in that the usually protective paralysis mechanism occurring during sleep is inappropriately activated.
• The opposite of this situation (failure to activate this protective paralysis) occurs in rapid eye movement behavior disorder.

Signs / Symptoms

• It is a muscular weakness which range from a barely perceptible slackening of the facial muscles to complete muscle paralysis with postural collapse.
• Attacks are brief, most lasting from a few seconds to a couple of minutes
• Typically involve dropping of the jaw, neck weakness, and/or buckling of the knees.
• They usually able to avoid injury because they learn to notice the feeling of the cataplectic attack approaching and the fall is usually slow and progressive.
• Speech may be slurred and vision may be impaired (double vision, inability to focus), but hearing and awareness remain normal.
• If the person is reclining comfortably, they may transition into sleepiness, hypnagogic hallucinations, or a sleep-onset REM period.

Cataplexy vs Narcolepsy

• Cataplexy worsens with fatigue
• Narcolepsy is usually, but not always, triggered by strong emotional reactions such as laughter, anger, surprise, awe, and embarrassment, or by sudden physical effort, especially if the person is caught off guard.
• Cataplectic attacks may occasionally occur spontaneously, with no identifiable emotional trigger.

• Cataplexy without narcolepsy is rare and the cause is unknown.

Mechanism

• Approximately 70% of people who have narcolepsy, and is caused by an autoimmune destruction of hypothalamic neurons that produce the neuropeptide hypocretin (also called orexin)
• Damage to orexin-secreting neurons in the hypothalamus can lead to inhibition of motor neurons, thus lowering muscle tone.

• Cataplexy is due to specific lesions in the brain that cause a depletion of the hypocretin neurotransmitter.
• Secondary cataplexy is associated with specific lesions located primarily in the lateral and posterior hypothalamus.
• Cataplexy due to brainstem lesions is particularly when seen in isolation.
• The lesions include
  • Tumors / Arterio-venous malformations of brain-stem (uncommon )
  • Ischemic / Traumatic events
  • MS
  • Paraneoplastic syndromes
  • Encephalitis
  • Lesions of the hypothalamus
• The neurological process behind the lesion impairs pathways controlling the normal inhibition of muscle tone drop, consequently resulting in muscle atonia.

Theories for episodes

A phenomenon of REM sleep, muscular paralysis, occurs at an inappropriate time. This loss of tonus is caused by massive inhibition of motor neurons in the spinal cord. When this happens during waking, the patient who had a cataplectic attack loses control of their muscles. As in REM sleep, the person continues to breathe and is able to control eye movements.

Hypocretin

The hypothalamus region of the brain regulates basic functions of hormone release, emotional expression and sleep. A study in 2006 in "Tohoku Journal of Experimental Medicine" concluded that the neurochemical hypocretin, which is regulated by the hypothalamus, was significantly reduced in study participants with symptoms of cataplexy. Orexin, also known as Hypocretin, is a primary chemical important in regulating sleep as well as states of arousal. Hypocretin deficiency is further associated with decreased levels of histamine and epinephrine, which are chemicals important in promoting wakefulness, arousal and alertness.