Restless legs syndrome (covered in Stage 9 from the movement disorder perspective) and periodic limb movement disorder are related conditions affecting both wakefulness and sleep architecture. They frequently co-occur in the same patient — approximately 80% of RLS patients also have PLMD detected on polysomnography.
RLS recap: the URGE criteria — uncomfortable urge to move legs, rest worsens, gets better with movement, evening/night onset. Diagnosed clinically based on history.
Periodic limb movements during sleep (PLMS): repetitive limb movements during sleep, typically involving extension of the big toe and flexion at ankle/knee/hip. Movements last 0.5-10 seconds and repeat at 5-90 second intervals throughout the night. Often unrecognized by the patient but reported by bed partners as "kicking" in sleep. Polysomnography is required for objective documentation.
PLMS vs PLMD: periodic limb movements are common (occur in many people without symptoms — increase in prevalence with age, present in many elderly without clinical impact). Periodic limb movement disorder requires both the polysomnographic finding AND clinically significant sleep disturbance or daytime impairment not better explained by another disorder. PLMS alone, without daytime consequences, doesn't necessarily warrant treatment.
The clinical overlap with RLS: most PLMD patients have or will develop RLS symptoms. The disorders share underlying pathophysiology — dopaminergic dysregulation, iron metabolism abnormalities. Treatment approaches overlap substantially.
Workup:
Iron evaluation first — ferritin <75 mcg/L warrants repletion (note: substantially higher threshold than for treating iron deficiency anemia). Brain iron stores can be inadequate when serum iron is normal.
Medication review — many medications worsen RLS/PLMD: serotonergic antidepressants (mirtazapine particularly), antihistamines (diphenhydramine), antipsychotics, anti-nausea agents (metoclopramide, prochlorperazine). Substitute or eliminate when possible.
Comorbidities: sleep apnea (often co-occurs and contributes to symptoms), peripheral neuropathy, end-stage renal disease (very high RLS prevalence), pregnancy (often dramatically worsens RLS, usually resolves postpartum).
Treatment hierarchy (modern):
Iron repletion first if ferritin low — oral if mild deficiency, IV iron for severe symptoms or oral intolerance.
Gabapentinoids (gabapentin enacarbil, pregabalin, gabapentin) as first-line pharmacotherapy — substantially shifted away from dopamine agonists due to augmentation risk.
Dopamine agonists (pramipexole, ropinirole, rotigotine patch) — historically first-line, but augmentation in 8-10%/year of use makes them second-line in modern practice. When used, monitor closely for augmentation.
Opioids for severe refractory cases — methadone, low-dose buprenorphine, oxycodone. Effective but require careful patient selection.
Augmentation — iatrogenic worsening of RLS by dopamine agonists — manifests as: earlier onset of symptoms during the day, increased severity, spread to other body parts, shorter time between dose and rebound. When recognized: switch to gabapentinoid, sometimes use opioids as bridge. This complication has driven the practice shift.
When you encounter a patient with RLS or PLMD symptoms, modern management starts with iron and gabapentinoids. Dopamine agonists are second-line. Comprehensive workup catches contributing factors. Treatment substantially improves sleep and daytime function.