Oh. . .Those Jerks!
Abstract & Commentary
Synopsis: Incidental leg movements during sleep are not associated with excessive daytime sleepiness, and increased sleepiness may reduce the likelihood of arousal from each leg movement.
Source: Chervin RD. Am J Respir Crit Care Med. 2001;164: 1454-1458.
This study from the University of Michigan retrospectively evaluated the association between incidental periodic leg movements of sleep (PLMS) and excessive daytime sleepiness. A group of 1124 patients with suspected sleep-disordered breathing that had undergone both overnight polysomnography (PSG) and multiple sleep latency testing (MSLT) were included for analysis. Self reported problem sleepiness and Epworth sleepiness score data were available for 873 and 201 patients, respectively. Subgroup analysis was performed on 321 patients for whom information on nocturnal arousals was available. There was no significant association between PLMS and objective or subjective sleepiness. In fact, objective sleepiness as measured by MSLT was less likely in patients with excessive PLMS (P = 0.03). Objective sleepiness was associated with higher apnea hypopnea index, severe sleep-disordered breathing, lower minimal oxygen saturation, and male sex (P < 0.001). The association of these variables with subjective sleepiness was less clear. The number of PLM-related nocturnal arousals predicted a decrease in objective daytime sleepiness (P = 0.008). These results cast doubt on 2 prevalent beliefs: that incidentally discovered PLMS may cause excessive daytime sleepiness, and that such PLMS are more likely to cause sleepiness when they are accompanied by nocturnal arousals.
Comment by Kevin L. Lewis, MD
PLMS, originally called "nocturnal myoclonus" and affectionately referred to in our center as "leg jerks," consist of rhythmical extensions of the big toe and dorsiflexions of the ankle with occasional flexions of the knee and hip that usually occur during the first part of the night and increase with age. Each movement lasts approximately 2-4 seconds with a frequency of about one every 20-40 seconds.1 During an overnight sleep study, PLMS are scored if they are part of a series of 4 or more consecutive movements lasting 0.5-5.0 seconds with an inter-movement interval of 4-90 seconds. A PLMS index of greater than 5 movements per hour of sleep is generally considered abnormal.2
PLMS are most commonly identified in association with other various sleep disorders. The most notable association is the occurrence of PLMS in the overwhelming majority of patients with the restless leg syndrome (RLS). RLS patients suffer from creeping and crawling sensations of the legs that are worse at night and at rest and get better with movement. This can lead to insomnia that, if severe enough, could cause excessive daytime sleepiness (EDS). It should be noted that RLS is a clinical diagnosis and does not require a sleep study. Most of what is known about PLMS comes from the study of RLS patients. However, PLMS can occur with the following: obstructive sleep apnea hypopnea syndrome (OSAHS), upper airway resistance syndrome (UARS), narcolepsy, and REM sleep behavior disorder.3,4 When patients with complaints of insomnia or hypersomnia have PLMS, and no other sleep disorder is present, they are referred to as having periodic leg movement disorder (PLMD). The cause of PLMS is not entirely clear, but there appear to be contributions from the spinal cord, peripheral nerves, and central dopamine and narcotic receptors.1,3 Patients with PLMD or with incidental PLMS in other sleep conditions often receive pharmacological treatment consisting of dopaminergics, benzodiazepines, or narcotics. With the exception of those patients who experience classic RLS symptoms, the treatment of PLMS/PLMD rarely improves insomnia or hypersomnia and leads to undesirable side effects including worsening of the original sleep complaint!
Despite the relatively common practice of treating PLMS/PLMD in the absence of RLS, there remains no compelling evidence that PLMS cause insomnia or hypersomnia. Nor is there evidence that treating PLMS reverses such complaints.3,5 Chervin has now added to the body of evidence that shows no relationship between PLMS and excessive daytime sleepiness.5 Although his study is limited to patients with sleep disordered breathing, it is incredibly relevant since this population represents the group that most commonly undergoes overnight polysomnography. It is satisfying that a large number of patients were studied, and there is data for objective and subjective sleepiness as well as arousals.
Because of studies like this, the use of scoring PLMS during a sleep study has come under fire. Furthermore, the diagnosis of PLMD may no longer have any usefulness. In fact, there was a pro-con debate on the very subject published in the same issue of the American Journal of Respiratory and Critical Care Medicine.6,7 Right now, it appears that the only reasonable time to consider treatment for PLMS is when they are associated with RLS. (Remember, a sleep study is not needed to make that determination). Said another way, "Just ignore those jerks!"
Dr. Lewis is a Fellow in Pulmonary, Critical Care, and Sleep Medicine at the University of Kentucky, Lexington, Ky.
References
1. Montplaisir J, Nicolas A, Godbout R, Walters A. Restless legs syndrome and periodic limb movement disorder. In: Kryger MH, Roth T, Dement WC, eds. Principals and Practice of Sleep Medicine. 3rd ed. Philadelphia, Pa: WB Saunders; 2000:742.
2. American Sleep Disorders Association. The international classification of sleep disorders (revised) diagnosis and coding manual. Rochester, MN. 1997.
3. Montplaisir J, et al. Sleep Medicine. 2000;1:163-167.
4. Exar EN, Collop NA. Sleep. 2001;24:188-192.
5. Chervin R. Am J Respir Crit Care Med. 2001;164: 1454-1458.
6. Walters A. Am J Respir Crit Care Med. 2001;164:1339.
7. Mahowald M. Am J Respir Crit Care Med. 2001;164: 1340-1341.