What is Cataplexy?

Overview

Our muscles are what powers our actions and movements. Could you imagine suddenly losing strength in any of your muscles and its impact on your daily life? 

Cataplexy is a condition in which people experience sudden and temporary muscle weakness or paralysis while they are awake. As the hallmark symptom of type 1 narcolepsy (also known as narcolepsy with cataplexy), cataplexy affects about 25-50 in 100,000 people.¹ 

Narcolepsy is a sleep disorder that causes excessive and irresistible daytime sleepiness in patients even after a full night’s sleep. Besides daytime sleepiness and cataplexy, narcolepsy patients can experience other symptoms such as:

• Hypnogogic hallucinations - hallucinations that happen as you go from wakefulness to sleep
• Sleep paralysis - a brief moment of inability to move or speak while falling asleep or waking up
• disrupted nighttime sleep - patients may wake up several times during the night and have poor sleep quality⁵

Causes of cataplexy

To understand what causes cataplexy, we have to introduce a protein called orexin, also known as hypocretin. Orexin is a protein produced by a group of neurons in the lateral hypothalamus of the brain. This protein has an important function in keeping us awake - it does so by suppressing rapid-eye movement (REM) sleep and the muscle paralysis that happens during REM sleep.

One sleep cycle comprises non-REM and REM sleep, and a full night of sleep is made up of approximately 4-6 sleep cycles. During REM sleep, your brain is about as active as when you’re awake, and dreams typically appear during this stage. Muscles are momentarily paralysed to prevent you from acting out the dreams. Orexin stops this muscle paralysis from happening when you’re awake. However, in patiens that have narcolepsy with cataplexy, there is a significant loss of orexin-producing neurons, causing orexin levels in the cerebrospinal fluid (CSF) to be too low to effectively suppress muscle paralysis. It was suggested that this loss of orexin-producing neurons could be an autoimmune condition.²

Aside from type 1 narcolepsy, cataplexy can also be caused by rare genetic disorders or as a side effect of certain drugs.³

Signs and symptoms of cataplexy

Cataplexy causes sudden and temporary muscle weakness or paralysis that can be really debilitating and even dangerous. According to the recount of many type 1 narcolepsy patients, cataplexy happenswhen they are experiencing strong emotions, particularly positive emotions, such as laughter.⁴ Some patients described that they get a feeling that they are about to lose muscle strength and can sometimes suppress it or lean against objects in time for support. Others have actually experienced falls due to the sudden muscle weakness in their limbs.⁴

The symptoms tend to begin in the head and neck. For example, patients may experience:

• Jaw dropping
• Twitching of facial muscle
• Head dropping

Sometimes, the muscle weakness extends down to the trunk and limbs, and causes symptoms such as buckling of the knees.²  

This momentary muscle weakness or paralysis affects both sides of the body, but can be partial or complete. Catapletic attacks usually last for a few seconds up to minutes, rarely for hours - in which case it would be called ‘status cataplecticus’.⁶ 

Early symptoms in children may differ from adults - instead of loss in muscle strength, children with cataplexy may experience abnormal movements and hypotonia.⁹

Management and treatment for cataplexy

As of now, cataplexy can only be managed by treating the symptoms with medications and lifestyle interventions. 

The recommended first-line medication that is used to control and treat cataplexy symptoms is sodium oxybate, which is a depressant of the central nervous system.⁹ Antidepressants, such as tricyclic antidepressants are also used to control cataplexy, despite some concerns over their efficacy and side effects.

Lifestyle interventions that can be helpful include having good sleep hygiene - for example:

• Avoiding caffeine intake several hours before bed
• Maintaining a regular sleep schedule with naps in between
• Avoiding smoking
• Getting sufficient exercise

Diagnosis of cataplexy

There are several ways to diagnose cataplexy:

1. Polysomnography - a sleep test used to observe sleep patterns, which also allows the assessment of nerve and muscles
2. Assay of orexin levels in CSF - cataplexy patients generally have low levels of orexin (<110 pg/mL) due to the loss of orexin-producing neurons⁶

FAQs

Who is at risk of cataplexy?

People with a family history are likely to have a higher risk for cataplexy - in some cases, the risk for narcolepsy with cataplexy for an individual with a family history could be as high as 40 times. The underlying reason for this could be genetic predisposition. Researchers have suggested the presence of certain gene variants (e.g. HLA DQB1*0602 allele) that could cause higher risks for narcolepsy with cataplexy.⁷ 

People with autoimmune disorders and brain injuries may also have higher odds of cataplexy.

One study in 2011 suggested that vitamin D deficiency might also contribute to higher risks for cataplexy. The researchers observed up to 5-fold higher odds for narcolepsy with cataplexy in the presence of vitamin D deficiency.⁸ 

How common is cataplexy?

Cataplexy is prevalent among patients with narcolepsy - about 75% of patients have this symptom.⁵ Approximately 0.06% of the adult population suffers from narcolepsy with cataplexy.⁶ 

How can I prevent cataplexy?

Cataplexy and narcolepsy are not preventable as patients could have underlying genetic predispositions or autoimmune conditions.  

When should I see a doctor?

You should seek medical advice as soon as possible if you suspect you have cataplexy so the symptoms can be managed promptly. 

Summary

Cataplexy is a debilitating symptom of the sleep disorder, narcolepsy, which causes transient loss of muscle strength and muscle paralysis. This symptom has been suggested to be associated with a significantly lower level of orexin protein in the brain due to the autoimmune destruction of orexin-producing neurons. Thus far, the recommended treatment for cataplexy is sodium oxybate, with antidepressants acting as debatable alternatives. You should visit your GP as soon as you can if you suspect you have cataplexy so that your symptoms can be better managed without a significant on your daily life.