Activity patterns of leg muscles in periodic limb movement disorder

The movements of leg muscles in reference to periodic limb movement disorder (PLMD) have only been described in global terms. The sequences of contracting muscles that cause the PLMs are said to be stereotypical. There is, however, doubt about this fixed sequencing in PLMD. Our goal was to define the sequence of muscle movements in PLMs and then analyse their patterns. We recorded with surface EMG all movements of the muscles said to be involved in PLMs (extensor digitorum brevis, EDB; tibialis anterior, TA; biceps femoris, BF; tensor fasciae latae; TFL) as well as the quadriceps (Q) and soleus (S) muscles in 12 patients with restless legs syndrome combined with PLMD. Accompanying polysomnography provided the sleep parameters. In total, 469 movements were analysed. In only 12% was there the appearance of the classic movement (EDB-TA-BF-TFL) or its direct variants. The most frequent sequences were characterised by contraction of only the TA, TA-EDB only, or TA-EDB followed by all other combinations (32%). The pattern EDB only, EDB-TA, or EDB-TA followed by contraction of one or more other muscles, was seen in 18%. All other combinations appeared in much smaller numbers or only once. Eight patients had specific patterns. Three consistently started with the same muscle. One patient always contracted all six muscles. Six patients never contracted more than three muscles. The number of muscles contracted correlated positively with the appearance of arousal from sleep. The interval between onset of contractions within the PLMs varied randomly in a range of 0-1 s. Within PLMs many variations of muscle movements were documented. Patterns were recognisable, individually determined, and related to arousal from sleep.