What is cataplexy?

Cataplexy is a very distinctive symptom, and with a clear history of cataplexy, the diagnosis of narcolepsy type 1 (NT1) is likely. However, establishing whether a patient truly has cataplexy can be complicated as many disorders can cause transient weakness and falls (Table 1). Complicating things further, other symptoms of narcolepsy such as fatigue and excessive daytime sleepiness can occur in many of these disorders, including functional neurologic disorders. Establishing a solid history of cataplexy is essential as both NT1 and functional neurologic disorders can both cause significant disability, but treatment approaches for these disorders are quite different.

Cataplexy is defined as episodes of muscle weakness triggered by strong, generally positive emotions [1]. It occurs almost exclusively in people with NT1, though it can occur in other rare disorders that injure the orexin/hypocretin neurons and their connections in the brainstem. Cataplexy is likely driven by the REM sleep atonia mechanisms that inhibit motor neurons, resulting in a loss of deep tendon reflexes during the episode. Classically, true cataplexy is triggered by strong, generally positive emotions like laughter, joking, or winning a game, though it can be triggered by intense anger and frustration. Cataplexy is often partial, affecting just the face, voice, and neck, without loss of axial tone, or it can be generalized, manifesting as a gradual slumping to the floor or chair with whole-body weakness. Cataplexy can begin with intermittent lapses in muscle tone that resemble tremors or asterixis, and episodes usually last <2 minutes. Importantly, consciousness is preserved during cataplexy, though longer episodes may transition into REM sleep.

Clinicians also describe “atypical” cataplexy which are true cataplexy episodes with unusual features. Atypical cataplexy may refer to episodes with unilateral weakness, no obvious trigger, or a clearly negative emotional trigger. The time course may also make these episodes “atypical” with hyperacute weakness and falls, or prolonged weakness as in status cataplecticus. Some people with established NT1 have both typical and atypical episodes [2]. One striking example of atypical cataplexy is the persistent facial and generalized weakness and drunken gait that can occur in the first years after NT1 onset in children [3].

In contrast, pseudocataplexy is a type of functional neurologic disorder that can mimic cataplexy. Functional neurologic disorders can cause debilitating and persisting neurologic symptoms but without clear underlying physiology [4]. Pseudocataplexy often manifests as episodes of sudden whole-body weakness, rather than just facial involvement [5], it may have unusual emotional triggers (often negative), and the feelings of weakness can persist for many minutes or hours. Importantly, deep tendon reflexes are preserved during an episode of pseudocataplexy. Cataplexy is primarily caused by inhibition of motor neurons, whereas pseudocataplexy may be caused by a failure to activate motor neurons.

These phenomena may be difficult to distinguish, and Menchetti and colleagues provide a helpful comparison of the clinical features of pseudocataplexy and cataplexy and evaluate psychiatric and personality traits associated with pseudocataplexy [6]. Though there was considerable overlap between true cataplexy and pseudocataplexy, the authors found that true cataplexy is most often associated with laughter (all respondents with cataplexy reported laughter as a trigger, compared with about one-third of respondents with pseudocataplexy) or telling a joke (47% of respondents with cataplexy, 13% respondents with pseudocataplexy). In contrast, pseudocataplexy was most commonly triggered by anger (67% of respondents). True cataplexy was heralded by facial involvement in 86% of people with cataplexy, whereas this occurred in only 40% of people with pseudocataplexy. More than half of pseudocataplexy episodes lasted longer than 2 minutes, but this was uncommon with cataplexy. As is reported in other functional neurologic disorders, pseudocataplexy occurs more commonly in women and is first developed at a later age than true cataplexy. People with pseudocataplexy also had higher levels of somatoform and affective symptoms.

For a diagnosis of NT1, confirmatory testing with either PSG/ MSLT or CSF orexin level is required. Menchetti et al. show that people with true cataplexy had shorter sleep latencies on MSLT than those with pseudocataplexy, but some people with pseudocataplexy also had positive MSLT findings. In these patients, CSF orexin level is especially useful, and it should be measured if there is suspicion of pseudocataplexy, as the orexin level would be normal.

Also, one should keep in mind that true cataplexy and pseudocataplexy can occasionally occur in the same person [2]. This sort of co-occurrence is not unusual in people with epilepsy who can also have non-epileptic spells [7], so sensitivity to this possibility may aid in both diagnosis and management of these different types of episodes.

This study by Menchetti is helpful, yet many questions about pseudocataplexy remain unanswered. As with other functional neurologic disorders, does pseudocataplexy improve with distraction when the patient focuses on something else? Are episodes associated with excessive slowness of thought and movement? What is its natural history over years? Is it associated with a history of childhood emotional neglect, trauma, stressors, and co-morbid psychiatric disorders such as PTSD, anxiety, and depression [8]?

These findings highlight the need for taking a careful and thorough history, as cataplexy cannot be distinguished by a history of transient weakness alone. Inquiring about a constellation of features should improve diagnostic accuracy. For example, the clinician should ask what triggers your weakness, which muscles feel weak, what are the functional consequences (e.g. inability to speak, dropping things from hands, need to sit down or fall), and how long do episodes last? If an episode occurs in clinic, one should test deep tendon reflexes (which are absent with partial and full cataplexy), look for facial weakness (e.g. ptosis, weak smile, etc.), and test if the weakness can improve with distraction.

Differentiating cataplexy and pseudocataplexy is critical both for accurate diagnosis and treatment. Cataplexy is almost always caused by NT1 and is usually treated with antidepressants, pitolisant, or oxybates. If pseudocataplexy is the recognized diagnosis, then it is important to educate people on this diagnosis and how it differs from NT1, stop any medications that are not indicated (eg, treatments for NT1), and refer to colleagues skilled in managing functional neurological disorders with methods including cognitive behavioral therapy, psychotherapy, hypnosis, physical rehabilitation, and psychiatry. Patients may also benefit from online resources such as https://www.neurosymptoms.org and https://www.fndhope.org [9]. This multidisciplinary and integrated approach helps avoid unnecessary treatments for NT1 and can improve the lives of people with pseudocataplexy.

Funding

The authors report no targeted funding.

Disclosure Statement

Financial Disclosure: T.E.S has received research grants from Takeda, Harmony Biosciences, and Jazz Pharmaceuticals. He has consulted for Avadel, Axsome, Consynance, Eisai, Harmony Biosciences, Idorsia, Jazz Pharmaceuticals, Merck, Orion Pharma, Takeda, and Tris Pharmaceuticals. M.S.B. has nothing to disclose. Nonfinancial Disclosure: M.S.B. and T.E.S have nothing to disclose.

COMMENTARY on “Phenomenology and psychiatric correlates of pseudocataplexy” by Menchetti, et al.

References