Cataplexy - Causes and Symptoms

Definition

Cataplexy is a sudden and transient loss of muscle tone, which occurs after a strong emotion. Stimuli that can trigger a cataplectic attack include laughter, fear, anger, surprise and excitement.

Cataplexy can manifest itself with a variety of physical changes, ranging from a barely perceptible weakening of the facial muscles, to the failure of the lower limbs, to complete atony. The subject loses voluntary control of the muscles and can fall to the ground, but always remains conscious and alert.

Cataplectic episodes can last a few minutes. After the cataplectic event, the person resumes normal muscle control.

Cataplexy occurs more frequently in times of emotional stress and in case of lack of sleep. The exact cause of cataplexy is however unknown. However, the weakness that occurs resembles the interruption of muscular activity that occurs naturally during REM sleep. Therefore, the sudden loss of muscle tone could be caused by an inhibition of the motor neurons in the spinal cord, due to a dysfunction of the sleep-wake cycle. Moreover, cataplexy is associated with reduced levels of hypocretin, a neuropeptide produced in the hypothalamus of primary importance in the regulation of the sleep-wake rhythm.

Cataplexy is one of the most common symptoms of narcolepsy, but it can also be associated with other pathological conditions. In particular, it may occur transiently or permanently for ischemic lesions, head traumas or tumors of the hypothalamus and brain stem. Other conditions in which it can be found include arteriovenous malformations and infections, such as encephalitis.

Cataplexy can also manifest itself as a side effect of the SSRI antidepressant withdrawal syndrome (selective serotonin reuptake inhibitors).