Periodic Limb Movements During Sleep (PLMS)
PLMS constitutes involuntary twitching of the lower leg or ankles during sleep, generally about once every 30 seconds or so. Movements tend to occur early after sleep onset, and last for a couple of hours until REM sleep commences when muscle relaxation occurs, but may occur later in the night also, often associated with snoring.
PLMS can be classified into two types.
- The presence of Snoring or Obstructive Sleep Apnoea can cause PLMS and twitchy movements as part of the arousal process.
- PLMS may occur independently of snoring and cause arousals from sleep which can be detected by small rises in the heart rate which each twitch, and can be clearly seen in the EEG if full polysomnography is being carried out.
Sufferers may have a principal complaint of daytime sleepiness with a raised Epworth Sleepiness Score as a result. Patients with Sleep Disordered Breathing who remain sleepy despite treatment with CPAP often have PLMS when restudied.
Bed partners will give valuable evidence of PLMS if they are kept awake by the sufferers condition. The periodic ‘twitch’ in the leg rocks the bed and keeps the partner awake, and may even force them into the other bedroom.
PLMS has a characteristic appearance if the heart rate is monitored overnight with a pulse oximeter. Small ‘jumps’ occur in the heart rate with each leg movement, and they tend to have a very characteristic pattern and regular occurrence in the trace. However, they have to be distinguished from the other common cause of this appearance which is Upper Airways Resistance Syndrome (UARS), although the rises are usually slightly less regular in that condition.
Attaching a set of leg electrodes to the front of each shin (pretibial region) will detect the electrical activity of each movement and, if the EEG is being monitored during Polysomnography, arousals will probably be seen in the brainwaves.
Where PLMS are occurring in association with snoring or sleep disordered breathing, that should be treated first, because the PLMS may resolve with the improvement in breathing on treatment.
Attention to sleep hygiene is also necessary, because PLMS are worsened by exhaustion in the same way that RLS is.
PLMS do not necessarily require treatment unless symptoms of daytime sleepiness are decreasing quality of life, or the relationship with the bed partner is suffering.
If there is no evidence of sleep disordered breathing, PLMS can be treated with tablets.