Restless Legs Syndrome (RLS), or Willis‐Ekbom Disease is a strange phenomenon, almost like a short-term craving or compulsion to move your legs.
It typically happens in the evening or nighttime hours when you’re sitting or lying down. Moving eases, the unpleasant feeling temporarily but its not painful, it just seems impossible to resist the need to move, fidget, stretch or walk around.
Periodic limb movement disorder (PLMD) is a condition ( formerly called sleep myoclonus or nocturnal myoclonus). It is described as repetitive limb movements that occur during sleep and cause sleep disruption (‘Sleep fragmentation). The limb movements, much like twitches usually involve the lower extremities, consisting of extension of the big toe and flexion of the ankle, the knee, and the hip. In some, upper extremities limb movements can also occur.
These twitches occur most frequently in light non-REM sleep (NREM). The repetitive movements occur at fairly regular intervals of 5 – 90 seconds. There can be significant night-to-night variability in frequency.
Periodic limb movement in sleep (PLMS) is not uncommon and observed in about 80% of those with RLS. PLMS can occur in over 30% of people aged 65 and older and can be asymptomatic. PLMS are very common in patients with narcolepsy and REM behaviour Disorder (RBD) and OSA, especially upon CPAP initiation.
True PLMD requires a diagnosis of periodic limb movements in sleep that disrupt sleep and are not accounted for by another primary sleep disorder including RLS, is uncommon. This needs a sleep test, OSA needs a home sleep test and Insomnia doesn’t need a sleep test if there is no evidence of anything else going on although it’s not always completely cut and dried.
We still have many diagnostic short-comings with true organic disorders though as even full overnight studies (polysomnographic – PSG) may not provide adequate evidence to classify insomnia, depression, and narcolepsy as separate entities.
PLMD has been less well studied than RLS and the exact prevalence or cause of either is unknown. It can occur at any age; however, it increases in prevalence increase with increasing age. Unlike RLS, PLMD does not appear to be related to gender.
As with RLS, some medical conditions are associated with PLMD. These include uremia, diabetes, iron deficiency (ferritin not just iron), OSA and spinal cord injury.