page_title: Cataplexy
section_title: Mechanism
hierarchical_section_title: Cataplexy / Mechanism
caption_attribution_description: English: Simplified diagram of a neural circuit involved in motor commands. Neurons in green are excitatory and red are inhibitory. 'α-MN' stands for w:alpha motor neuron (the innervation of which or lack thereof is the result of the circuit), 'AMYG' w:amygdala, 'LH' w:orexin neurons in the w:lateral hypothalamus, 'LC' w:locus coeruleus, and '(int)' stands for various interneurons.
context_page_description: Cataplexy is a sudden and transient episode of muscle weakness accompanied by full conscious awareness, typically triggered by emotions such as laughing, crying, or terror. Cataplexy affects approximately 70% of people who have narcolepsy, and is caused by an autoimmune destruction of hypothalamic neurons that produce the neuropeptide hypocretin, which regulates arousal and has a role in stabilization of the transition between wake and sleep states. Cataplexy without narcolepsy is rare and the cause is unknown.
  The term cataplexy originates from the Greek κατά, and πλῆξις and it was first used around 1880 in German physiology literature to describe the phenomenon of tonic immobility also known as "playing possum". This animal is able to feign death when it is threatened. In the same year the French neuropsychiatrist Jean-Baptiste Gélineau coined the term 'narcolepsy' and published some clinical reports that contain details about two patients who have similar condition as the narcoleptic cases nowadays. Nevertheless the onset reported by him was in adulthood as compared to the nowadays cases reported in childhood and adolescence.
context_section_description: Cataplexy is considered secondary when it 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 uncommon particularly when seen in isolation. The lesions include tumors of the brain or brainstem and arterio-venous malformations. Some of the tumors include astrocytoma, glioblastoma, glioma, and subependynoma. These lesions can be visualized with brain imaging, however in their early stages they can be missed. Other conditions in which cataplexy can be seen include ischemic events, multiple sclerosis, head injury, paraneoplastic syndromes, and infections such as encephalitis. Cataplexy may also occur transiently or permanently due to lesions of the hypothalamus that were caused by surgery, especially in difficult tumor resections. These lesions or generalized processes disrupt the hypocretin neurons and their pathways. The neurological process behind the lesion impairs pathways controlling the normal inhibition of muscle tone drop, consequently resulting in muscle atonia.
caption: In this simplified brain circuit, damage to orexin-secreting neurons in the hypothalamus can lead to inhibition of motor neurons, thus lowering muscle tone.
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