Cramp-fasciculation syndrome: muscle twitching and cramps explained

A fasciculation is a small, brief twitch of a muscle that can be seen under the skin or felt. A cramp is the sudden, involuntary, painful contraction of a muscle. When the two occur together, and examination finds no muscle weakness, the combination is usually called benign cramp-fasciculation syndrome.

The NHS Scotland Right Decisions guidance for GPs describes muscle fasciculation as usually seen or felt, most commonly in the calves and after exercise, but sometimes more widespread. It says fasciculations can be associated with cramps and, in the absence of weakness, are usually benign cramp-fasciculation syndrome, and that they are nearly always benign.

It also notes that a family history is common in benign cramp-fasciculation syndrome, which can be reassuring to know when you are looking for patterns in your own family.

The NHS describes leg cramps as common, usually harmless and only lasting a short time. It says they can last from a few seconds to 10 minutes, usually affect the calf, and that the muscle may feel sore for up to 24 hours afterwards. Most people have them at night or when resting.

The NHS lists possible causes including ageing, putting too much strain on muscles during exercise, pregnancy, certain medicines such as statins or diuretics, dehydration and liver disease from drinking too much alcohol, and says the reason for some cramps is unknown. The Right Decisions guidance adds that cramps are commonly worsened by exercise, dehydration or pregnancy, and that profound cramps, or those associated with other symptoms such as weakness, may occasionally indicate underlying neuromuscular disease.

Twitching is a symptom people often search for with fear, because twitches and muscle cramps are listed among early symptoms of motor neurone disease (MND). The NHS MND page says that early symptoms such as twitches and muscle weakness can be similar to other, less serious conditions, but it is important to get them checked by a GP. It lists stiff or weak hands, weak legs and feet and difficulty gripping among the first symptoms.

The key distinction in the guidance is weakness. The Right Decisions factsheet says the question to ask is whether there is any weakness, and that if there is, referral is appropriate. Isolated fasciculation, with a normal examination, is common and most people will be reassured by careful explanation.

The guidance also acknowledges that this can evolve into health-related anxiety, which in turn can amplify fasciculation, creating a cycle. It says explicit explanation and avoiding repeated reassurance is helpful, and that severe cases may need treatment of the health anxiety itself.

The Right Decisions factsheet lists the questions a GP is encouraged to ask: is there any weakness, is there a family history, is the person taking medicines that might cause electrolyte imbalance (such as diuretics or methylphenidate), and do symptoms occur only at night, in which case restless legs syndrome might be considered. It also asks what the person is worried about.

Tests suggested in primary care are a biochemical screen including urea and electrolytes, calcium and thyroid function tests, and creatine kinase. A small rise in creatine kinase above the reference range is rarely relevant.

For fasciculation the guidance says treatment is explanation and reassurance, and if it is severe, treatment of health anxiety. For cramps it lists calf muscle stretches before bed, reducing diuretics and caffeine where applicable, and medicines such as vitamin B complex, diltiazem or a short course of quinine in some cases. The NHS adds that quinine tablets are not suitable for everyone and a GP will discuss risks and side effects.

The NHS suggests stretching the calf muscles regularly, standing and putting weight on the leg during a cramp, and says paracetamol or ibuprofen may ease soreness after a cramp but will not help while it is happening.

The NHS says to see a GP if leg cramps are disturbing your sleep, you also have numbness or swelling in your legs, or cramps last longer than 10 minutes. The NHS MND page says to see a GP if you have twitches or muscle cramps that keep happening, last a long time or do not go away, or if you have difficulty holding or gripping objects or weakness in your legs or feet.

The Right Decisions factsheet says neurology advice is appropriate for any wasting or weakness, very florid or widespread fasciculation, fasciculation with severe cramp, or unusually profound or debilitating cramps. If a GP thinks MND is possible, the NHS says they may refer you to a neurologist for an assessment and tests.