• Periodic limb movement syndrome
• sleep disorder

Patients with periodic limb movement syndrome (PLMS) experience a series of involuntary leg movements at sleep onset and during sleep. The movements are rhythmic or jerky and range from simple extension of the big toe to movement of the whole leg, with flexion of the knee and hip. They generally occur every 20–40 seconds and last 0.5–5 seconds.

A 65 year old woman was referred to our department for differential diagnosis of suspected sleep apnoea syndrome. At presentation she reported excessive daytime sleepiness and mild snoring. Polysomnography revealed PLMS of both legs, with an index score of 89 (fig 1). When the condition was explained to her, she reflected for a moment and said, “now I know why I can always tell which way around my sheets go on my bed”.

The patient later brought in a fitted terry bedsheet with two well worn areas at one end, corresponding to the position of her feet in bed (fig 2). Ad hoc exmination of a new terry sheet showed that repeated rubbing rapidly causes noticeable roughening of the surface. With continuing wear the fabric gradually becomes threadbare and finally tears.

Bedding in disarray is a well known feature of PLMS. The increased use of fitted terry sheets may offer a new diagnostic sign for this syndrome—discrete areas of wear from foot movement in bed.

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Figure 1

Four minute section of polysomnograph tracing showing periodic movements of both legs (circle).

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Figure 2

The patient reported that she replaces about four bedsheets every year because they wear out near the bottom.