He was admitted to the epilepsy monitoring unit. On exam, he had mild chorea affecting distal upper extremities, not involving legs, normal attention and cognition, but poor insight. Video EEG captured two types of episodes. Both emerged after arousals during non-REM (NREM) sleep. The first was limited to brief, apneic arousals with snoring and consisted of an apneic “jerk” and emergence of generalized chorea that lasted for 10 to 30 seconds before returning to NREM sleep (Fig. 1A; see Video 1, type A). The second occurred after more sustained awakenings with repetitive ballistic movement (RBM) consisting of quasi-rhythmic (0.5–2.0 Hz) violent movement of legs (Fig.1B; see Video 1, type B). No other sleep-related movements and no epileptiform discharges were present. An arousal index of 70 arousals per hour was calculated during a 1-hour sample, most associated with probable apneas. No evidence of REM movements or absence of atonia occurred; in fact, only a few epochs of REM or deep sleep were evident, with most sleep consisting of N1/N2.
Figure 1. Two 30-second samples of video EEG; standard 10 to 20 electrode placement. (A) Post-arousal chorea during NREM sleep: an apneic arousal (arrow) leads to cessation of apnea and emergence of chorea. (B) Twenty seconds after sample (A), repetitive ballistic movement of legs appear (arrows)
Formal polysomnography (PSG) performed 6 weeks postdischarge showed that RBM did not occur during REM and primarily occurred in arousal after events in NREM sleep. A follow-up visit 5 months later revealed that treatment with continuous positive airway pressure improved nocturnal movements.
We found two nocturnal movements associated with arousals or awakenings: the first typical chorea, the second RBM. The case is of interest for the following reasons. First, RBM has not been previously described as a sleep-related movement disorder in HD. Second, both chorea and RBM occurred during the waking state subsequent to arousals and attenuated with sleep similar to other movement disorders, such as tremor. Third, diagnosis of nocturnal movements and the cause of fragmented sleep required overnight video EEG monitoring for characterization, leading to the recognition that a typical sleep disorder—probable obstructive sleep apnea—triggered awakenings and abnormal movements.
Although motor and cognitive symptoms of HD are well described, its sleep disorders are less so. Animal models of HD demonstrate fragmented sleep with circadian disorganization (see Morton). Survey instruments show disturbed sleep and excessive sleepiness.PSG findings in humans with HD can be confounded by medications that change sleep architecture and may be difficult to perform because of chorea and dementia. However, the present case shares features of disordered sleep described in HD, including frequent awakenings/arousals, diminished REM, and lack of ultradian NREM-REM cycles.[1, 3-5] Other problems include delayed sleep-onset latency, increased periodic limb movements, and REM behavior disorders.[3-5] Although these reports emphasize associations with the primary degenerative process, the present case suggests that identification of common causes of arousals can lead to clinical benefits in HD.
The prevalence of nocturnal chorea in HD is unclear. Our findings agree with a previous study that found that chorea emerged during arousals. On the other hand, others found that, although motor activity was increased during sleep, chorea did not account for the preponderance of movements,[5, 7] although diagnosing chorea by actigraphy may be difficult.
This is the first report of RBM in HD. RBM can fall into one of two nonexclusive categories. First, RBM may represent an element of hyperkinesia in HD, with chorea as the typical and RBM as the severe expression. However, in this patient, RBM was present before onset of chorea. On the other hand, RBM resembles rhythmic movement disorder, such as jactatio capitis nocturna (head banging). Though RBM is quasi-rhythmic in morphology, we feel that the term “repetitive” is a more accurate descriptor of the movement than “rhythmic”. RBM shares with rhythmic movement disorder (1) a tendency for occurrence in those with cognitive impairment, (2) quasi-rhythmic movements of 0.5 to 2.0 Hz, and (3) expression during both wakefulness and sleep-wake transitions (although unlike head banging, RBM did not occur during sleep).
We speculate that because sleep is not well characterized in HD, nocturnal movement disorders may be more pervasive than recognized. What is clear, however, that for movements that are triggered by arousals, measures to diagnose reversible causes of sleep fragmentation can lead to effective treatment.