Reply to Piano et al.

To the Editor: Piano et al. recently found a higher periodic leg movements (PLM) index during wake and sleep in 30 patients with advanced Huntington’s disease (HD) than in the control group (17.6 ± 19.4 PLMs vs. 0.5 ± 1.0) [1]. Now, they ask whether these periodic movements could primarily cause the arousal-related abnormal movements that we recently reported in 29 patients with HD [2]. In our video-clips, a few arousals started with bilateral limb flexion movements. They were, however, not simple (they constituted complex, target-oriented movements, suggestive of repositioning behaviors), not stereotypic (severe opisthotonos-like as well as bruxism were observed), and, most important, these movements were not periodic (according to the PLM definition, which includes series of at least four 0.5–10 second long limb movements, separated by 5–90 seconds [3]). Consequently, these movements cannot constitute PLMs followed by a complete awakening and behaviors. In our first series of 25 patients with HD, the PLM index was slightly higher in patients than in controls (9 ± 11 vs. 2 ± 5), but still within normal values (below 15) and not causing frequent arousals [4]. If we pool together the 43 patients with HD monitored by our consortium, this difference with controls disappears (Table 1). Thus, PLMs seem to be motor manifestations of HD in older, more severe patients (with more frequent treatmentinduced PLMs) rather than in patients with very mild to moderate HD (see Table 1 for comparison of both cohorts). Our data cannot support the concept of a periodic motor (or even cortical) activity as a background for this abnormal motor activity upon arousals. Rather, one may imagine that any cause of arousals (possibly PLMs in aged patients, but also apnea, or simply ambient noises, but nothing necessarily periodic) could trigger them because they resemble a transient exacerbation of choreic movements upon arousal.