Behavioural and neurophysiological correlates of human cataplexy: A video-polygraphic study
Introduction
Cataplexy is best defined as a transient loss of muscle tone triggered by strong emotions and typically occurring while laughing or joking (Krahn et al., 2005). It is a core symptom of narcolepsy with cataplexy (NC), and is most often present at disease onset (Gélineau, 1880, Okun et al., 2002, American Academy of Sleep Medicine, 2005). Although cataplexy can result in a dramatic and complete loss of postural muscle tone, resulting in a fall with complete paralysis, loss of tone is more often partial, affecting only some muscles. In these cases it may result in head nodding, limb weakness, slurred speech or facial muscle flickering. Facial attacks with tongue protrusion and closure of eyelids (“cataplectic facies”), are often found around disease onset, sometimes without any clear emotional precipitants (Plazzi et al., 2006, Plazzi et al., 2008, Serra et al., 2008). Generalized forms leading to falls are reported by 25% of NC patients (Bassetti and Aldrich, 1996, Sturzenegger and Bassetti, 2004).
Behavioural and polygraphic criteria for cataplexy have recently been suggested for a murine model of narcolepsy, in which cataplexy is obviously not emotionally triggered (Scammel et al., 2009). By contrast, polygraphic or video-polygraphic studies of cataplexy in human narcolepsy are few and have shown a complex mixture of suppression and enhancement of EMG activity in different muscular segments resulting in postural instability if not falls in some cases (Scollo-Lavizzari, 1970, Guilleminault, 1976, Rubboli et al., 2000, Donadio et al., 2008, Serra et al., 2008).
Cataplectic attacks may last from a few seconds to minutes, and their duration can be prolonged by emotional stimuli (i.e. by reiteration of the trigger, intervention of helpers). Attacks of long duration may evolve into a frank REM sleep episode. In rare cases, cataplectic spells may occur in tightly packed clusters, or be almost continuous, a condition known as “status cataplecticus”. This particular condition may appear at the onset of the disease or may be provoked by antidepressant withdrawal (Plazzi et al., 2007, Serra et al., 2008). Unfortunately, it is at risk of being mistaken for a psychogenic symptom (Simon et al., 2004).
Cataplexy has long been thought to represent the abnormal expression of REM sleep, whereby muscular atonia typical of REM sleep occurs inappropriately when awake (American Academy of Sleep Medicine, 2005). Some features of cataplexy, however, do not fully conform to this view (Tucci and Plazzi, 2009). This study is a video-polygraphic analysis of cataplexy in a group of patients with well characterized NC. Our goal was to investigate the behavioural features, the EMG pattern of cranial and skeletal muscles, and autonomic and EEG variables during cataplexy to shed more light on this puzzling symptom.
Section snippets
Patients
Seven patients (2 women) suffering from excessive daytime sleepiness and unequivocal cataplexy were included. All fulfilled the diagnostic criteria for NC (American Academy of Sleep Medicine, 2005) and gave informed consent. Non-structured clinical interviews and a preliminary polysomnography (PSG) using the MESAM IV® system (Peter and Penzel, 1994) were used to exclude sleep-related breathing disorders and significant oxygen desaturations. This was followed by a 48 h PSG using a VITAPORT®
Results
Eighty-five cataplectic attacks were recorded overall in the seven subjects, all of them classified on the basis of their behavioural aspects. Forty-four episodes (52%) resulted in a complete collapse of the patient to the ground; the remaining 41 were more restricted and classified as segmental (i.e. without body fall). Twenty of the 44 cataplectic attacks that ended with a complete collapse of the patient to the ground were preceded by segmental cataplectic attacks (see below).
Discussion
Multiple cataplectic attacks were elicited under audiovisual and polygraphic monitoring in seven drug-free patients. In segmental cataplectic attacks, EMG silencing appeared irregularly and “focally” on masticatory, facial, neck, axial or limb muscles, brief in duration (less than 300 ms) and often associated with a flapping, downward motion of the relative joints. Because of a possible concomitant occurrence of atonia in antagonistic muscles, these focal and partial lapses of postural control
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