Restless legs and limb movements

Two related things happen to legs at night, and they are routinely confused with each other.

Restless legs syndrome is an unpleasant sensation deep in the legs, with an overwhelming urge to move them. It happens while awake, mostly in the evening and when sitting or lying still, and moving relieves it immediately — which is the feature that distinguishes it from almost everything else. It is common, affecting something like one adult in twenty to a degree worth treating, and it is substantially under-diagnosed.

Periodic limb movements in sleep are repetitive jerks or upward flexing of the foot and ankle during sleep, in runs that repeat every twenty to forty seconds and can go on for hours. The person asleep is generally unaware of them. A bed partner is usually the one who notices.

Most people with restless legs also have the limb movements. Many people with the limb movements have no restless legs and no symptoms at all. The practical difference is that restless legs is a condition with a diagnosis and effective treatment, while limb movements alone are usually a finding rather than a problem.

What restless legs actually feels like

Descriptions vary and all of them are approximations: crawling, creeping, pulling, aching, fizzing, something moving under the skin, an electrical restlessness. It is felt deep inside the limb rather than on the skin, usually in the calves and thighs, sometimes in the arms, and it is often hard to put into words — which is one reason people do not raise it with a GP.

The four features that define it are worth setting out, because they are what a diagnosis rests on:

• An urge to move the legs, usually with uncomfortable sensations.
• It begins or worsens during rest or inactivity.
• It is relieved, at least partly, by movement — walking, stretching, pacing.
• It is worse in the evening or at night than during the day.

No scan or blood test establishes it. It is diagnosed on that description, which means a clear account of the symptoms is the whole of what a GP needs. Sleep studies have no routine role: they are for cases where something else is suspected, not for confirming restless legs. Older writing that sends people for a night in a sleep laboratory is describing how the limb movements are measured, not how restless legs is identified.

Why it happens

Rather more is known than used to be. Restless legs involves the brain's handling of iron and of dopamine, and there is a strong genetic component — most people with the primary form have a family history, often undiagnosed in the relatives.

It is also frequently secondary to something else, and this is where the useful action lies:

• Low iron stores, which is the single most important thing to look for. Iron can be low enough to cause restless legs without anaemia, so a normal blood count rules nothing out.
• Pregnancy, where it is common, usually worst in the third trimester, and usually settles after delivery.
• Kidney disease, particularly in people on dialysis, where it is very common.
• Diabetes and peripheral neuropathy.
• Medicines, discussed below.

Caffeine, alcohol and nicotine all make it worse, and so does sleep deprivation — which creates a loop, since restless legs causes sleep deprivation.

The medicines that cause it

This belongs near the front rather than buried at the end, because a drug cause is both common and easily reversed, and because several of the culprits are things people take for sleep.

Sedating antihistamines — the active ingredient in most over-the-counter sleep aids, and in many cold and allergy remedies — are a well-recognised trigger. So are a number of antidepressants, including the commonly prescribed ones and mirtazapine in particular; antipsychotics; and anti-sickness medicines such as metoclopramide and prochlorperazine.

There is an unpleasant irony in the first of those. Someone sleeping badly because of restless legs buys an over-the-counter sleeping tablet, and the tablet makes the restless legs worse.

None of these should be stopped without advice, and several of them are being taken for conditions that matter more than the legs. But the connection is worth raising, because an alternative often exists.

Treatment, starting with iron

Anyone with troublesome restless legs should have their iron stores checked — ferritin and transferrin saturation, ideally on a morning sample taken before any iron supplement that day. The threshold used for treating is higher than the one used for diagnosing anaemia: iron replacement is given when ferritin is below about 75 to 100 micrograms per litre, which is well inside what a laboratory report would call normal. Where iron is low, the cause of that also needs establishing.

Correcting iron resolves or substantially improves symptoms in a good proportion of people, and it is the only treatment that addresses a cause rather than suppressing symptoms. Iron should not be taken on spec, though: taking it without a low result does nothing useful and can do harm.

Non-drug measures are worth trying in mild cases and alongside anything else: moderate regular exercise, which helps, as against overexertion, which does not; stretching, walking or a hot bath in the evening; leg massage; cutting caffeine, alcohol and nicotine; and treating any untreated sleep apnoea, which makes restless legs worse. Pneumatic compression devices have some evidence behind them. Standing up and walking about during a long flight or a long meeting is the oldest remedy there is and remains a good one.

Where medication is needed, UK practice has changed substantially, and this is the part of the subject where older writing is now actively misleading.

The current first choice for frequent or daily symptoms is a medicine from the gabapentinoid group — gabapentin or pregabalin — at a low starting dose, lower again in older people. They are used outside their licensed indications for this purpose, which is normal and worth knowing. The main drawbacks are drowsiness and unsteadiness, which increase with dose.

Dopamine agonists — pramipexole, ropinirole, and rotigotine as a patch — work extremely well at first and are no longer recommended as the first option. The reason is augmentation: over months and years the condition paradoxically worsens, with symptoms starting earlier in the day, becoming more intense, and spreading to the arms and trunk. The instinctive response is to increase the dose, which accelerates the process. In long-term follow-up, more than half of people on these medicines develop it. They also carry a risk of impulse control problems — compulsive gambling, spending, eating or sexual behaviour — which people are not always warned about and which can be severe.

These medicines still have a place, at the lowest dose and with the possibility of augmentation understood from the start. Anyone already taking one whose symptoms have been getting worse rather than better should raise augmentation specifically, because the worsening is easily read as the condition progressing and treated with more of the drug. They also should not be stopped abruptly, as that causes a severe rebound.

Where restless legs is painful, a weak opioid is sometimes used. Benzodiazepines, which older writing names first, are not a treatment for restless legs: they sedate through the symptoms without touching them, and bring dependence with them.

The limb movements on their own

Periodic limb movements found without restless legs and without daytime consequences generally need no treatment. They are common, they increase with age, and in the great majority of cases the person sleeping through them comes to no harm.

They matter in two situations. Where they are frequent enough to fragment sleep and the days are genuinely affected, they are worth investigating. And they are often a sign of something else — restless legs, sleep apnoea, iron deficiency, kidney disease, narcolepsy, or one of the medicines listed above — which is the more useful thing to look for than the movements themselves.

The commonest consequence is to the bed partner, who may be losing considerably more sleep than the person moving. Separate beds or separate rooms are a reasonable and underused answer to that, and no reflection on anybody.

When to see a GP

• Leg sensations with an urge to move that are disturbing sleep or spoiling evenings — this is treatable, and specifically worth the appointment.
• Before assuming it is just cramp or ageing. Cramp is a painful visible contraction that movement does not relieve; restless legs is a sensation that movement does.
• If taking anything from the list of medicines above, so an alternative can be considered.
• In pregnancy, where iron is the first thing to check and most drug treatments are avoided.
• If already on a dopamine agonist and symptoms are starting earlier in the day, intensifying, or spreading — without stopping the medicine first.
• If any compulsive behaviour has developed since starting a dopamine agonist, which is urgent and is rarely connected by the person to the tablets.
• If limb movements at night come with loud snoring, pauses in breathing, or daytime sleepiness, which points at sleep apnoea.