Muscle Cramps

Cramp usually means " a spasmodic, painful, involuntary, contraction of skeletal muscle."¹ and there are many causes. This transient, involuntary episode of pain, is usually sustained for minutes and even up to 10 minutes, and whole muscles or muscle groups go into spasm. The lower limbs are almost invariably involved.

The prevalence increases with age. About a third of people over 60 and half those over 80 complain of cramps.² The problem is often distressing and has an adverse effect on quality of life.

Muscle cramps are very common and probably we have all experienced them at some time. When patients complain of cramps it is important to ascertain exactly what they mean as the term is frequently used to describe any tight pain of muscular origin. No one definition of muscle cramp exists, and many classifications of muscular cramps have been attempted.

Cramps may be grouped according to their underlying aetiology:

• Paraphysiological cramps
• Symptomatic cramps
• Idiopathic cramps

Find out what the patient means by cramps:

• Where do they occur? When do they occur? How often?
• How long do they last?
• Is there any other medical history?
• Are drugs taken?
• Ask about alcohol consumption
• Ask about sport

Most often cramps involve the calf muscle, thigh muscle, and small muscles of the foot. Of these, the most commonly affected is the calf and it tends to be unilateral. They occur at rest and usually at night. The most likely explanation is that leg cramps occur when a muscle that is already in a shortened position is involuntarily stimulated. This commonly happens at night where the plantar flexed foot places the calf and ventral foot muscles in the most shortened and vulnerable position. The cramp may last seconds or minutes but the muscle may be tender for the next 24 hours.

• During an attack the affected muscle or group is hard and tender.
• Between attacks examination is unlikely to be rewarding.
• The muscle may be tender for up to 24 hours after the last attack.
• In the elderly or where peripheral vascular disease is suspected, check peripheral pulses.
• This may be due to neurological disease but it is unlikely that undiagnosed neurological problems will emerge. However, if there is reason to suspect, perform a neurological examination of the lower limbs.

Paraphysiological cramps occur in healthy people in response to a physiological stimulus. They are very common and may occur during sport or in unaccustomed exercise. They are especially likely to occur during endurance sports. They are thought to be the result of hydro-electrolyte imbalance following repeated and chronic use of the same muscle group producing increased excitation of the neuromuscular nerve endings.³ It is thought that low levels of magnesium and other electrolytes may also play a part.

Paraphysiological cramps are also very common in pregnancy occurring in almost half of all pregnant women at some stage, particularly in the third trimester. The aetiology in pregnancy is unknown. Pressure on the nerves and blood vessels, circulatory changes, and low levels of calcium and magnesium have all ben suggested. The use of magnesium supplements has been studied and appears to have some effect when used in pregnancy,⁴ although it is probable that more than one factor is responsible for the muscle cramps.

Paraphysiological cramps may also occur in healthy individuals as a result of a sustained posture over a prolonged period of time.

Cramps may also occur in association with metabolic disturbance including hyponatraemia, hypokalaemia, hyperkalaemia, hypocalcaemia, hypomagnesaemia, hypoglycaemia. One or more of these may be the underlying aetiology in many of the caused listed below. Blood tests measure the extracellular environment but the intracellular fluid is probably more important.

• Arterial insufficiency
• Acute or chronic diarrhoea
• Excessive heat and sweating causing Na depletion
• Hypothyroidism is associated with weakness, enlarged muscles and painful muscle spasms
• Hyperthyroidism may be associated with myopathy
• Pregnancy, especially in the late months
• Lead poisoning
• Sarcoidosis
• Hyperparathyroidism (hypercalcaemia)
• Heavy alcohol ingestion, which may induce severe muscle cramps, as may cirrhosis
• Hyperventilation induced respiratory alkalosis
• Haemodialysis, possibly due to reduced circulating volume
• Disorders of the lower motor neurone, including amyotrophic lateral sclerosis, polyneuropathies involving the motor neurone, recovered poliomyelitis, peripheral nerve injury and nerve root compression

Drugs

In a study of 70 patients in general practice who were prescribed quinine for cramps, 37 (53%) were also taking drugs known to cause cramps.⁵ Implicated drugs include:

• Salbutamol and terbutaline
• Raloxifene
• Opiate withdrawal
• Diuretics cause electrolyte loss
• Nifedipine
• Phenothiazines
• Penicillamine
• Nicotinic acid

Idiopathic means of unknown cause and so it is a diagnosis of exclusion. However, this represents the largest group of causes of cramps and it is the subject of Clinical Knowledge Summaries guidance. Familial forms exist which appear to have an autosomal dominant mode of transmission.⁶ This group also contains conditions such as idiopathic nocturnal cramps and fasciculation-cramp syndrome.

The differential diagnoses for leg cramps will include:

• Restless legs (Ekbom's syndrome)
• Intermittent claudication and ischaemic rest pain
• Muscle injury or strain
• Hypnagogic muscle jerking (when falling asleep)
• Lumbar nerve root entrapment
• Ruptured Baker's cyst
• Deep vein thrombosis or thrombophlebitis
• Peripheral neuropathy
• Occupational cramps such as writer's cramp or musician's cramp are focal dystonias and usually affect the upper limb

Usually no investigation is indicated. They may be performed if an underlying cause is suspected.

Potential investigations include:

• U&E
• Liver function tests
• Thyroid function tests
• Serum calcium or magnesium
• Creatine kinase if a myopathy is suspected
• Lead levels if plumbism is suspected

In most cases the aetiology is benign and the patient needs to be reassured of this whilst steps are taken to help alleviate the problem. Exclude known causes of muscle cramps without excessive and unnecessary investigation.

Management depends upon the cause of the problem. Review drugs. If it is a correctable problem, this should be addressed. This may include the use of diuretics and electrolyte imbalance. Asking patients to keep a sleep and cramp diary may be helpful to assess progress.⁷

Non-drug

The evidence base for management of this common but usually benign condition is not very strong.

• Passive stretching and massage of the affected muscle will help ease the pain of an acute attack.
• It is thought that regular stretching of the calf muscles throughout the day may help to prevent acute attacks. Some people recommend stretching 3 times daily whilst others advocated stretching before going to bed.
• Using a pillow to raise the feet through the night, or raising the foot of the bed may help to prevent attacks in some people.⁸

Drugs

• Quinine sulphate remains the drug of choice for the treatment of leg cramps in non-pregnant individuals who have not responded to conservative measures.¹¹
• Many people are prescribed quinine for many years but the long term efficacy is unproven.
• Several other drugs have been suggested as possible treatments including diltiazem,¹² verapamil,¹³ and naftidrofuryl.¹⁴
• In old people with hypertension a double blind RCT found significant benefit from vitamin B complex.¹⁵
• Vitamin E is ineffective.¹⁶
• Magnesium supplements may help relieve the symptoms in pregnant women who have not responded to conservative measures.¹⁷ Avoid quinine in pregnancy and concentrate on massage and stretching rather than drugs.
• Various treatments have been used in pregnancy.
  • Calcium lactate is ineffective.
  • The benefit of multivitamins is uncertain. It may have been a placebo response.
  • Sodium chloride may be beneficial although the trial was over 50 years ago and the potential of added salt to cause hypertension may cause concern.

Quinine appears to be the "gold standard" for treatment but should be used with care in the elderly and those on dialysis and avoided in pregnancy and liver disease.¹⁸ Various forms of "complementary and alternative" therapies are available and bearing in mind the natural history for resolution and the placebo effect, each will claim its own successes and ignore its failures.