Restless leg syndrome (RLS) was initially considered by some to be due to a disorder of the blood vessels or nerves in the legs. However, both these reasons have been rejected. The exact cause of restless legs syndrome (RLS) is not yet known. The current hypothesis is that RLS is caused due to abnormalities in brain chemicals (neurotransmitters) which control muscle movements, or the automatic movements. Studies are being done to understand the exact cause of RLS.
RLS can be primary or idiopathic (caused due to no known cause) or secondary (caused due to some underlying disorder). The prevalence of primary RLS is higher than secondary RLS.
Primary RLS: The cause of primary or idiopathic RLS is not known but some of the risk factors are heredity, psychiatric factors, stress, and fatigue.
- Heredity: Experts consider that RLS runs in families in about 50% the people with RLS. This specifically applies when the condition starts at an early age. Some probable sites on the chromosomes where genes for RLS may be present have been recognised.
- Others: Symptoms of RLS worsen due to psychiatric factors, stress, and fatigue.
- Secondary RLS: Several medical conditions have been known to cause secondary RLS.
- Iron deficiency Anaemia and Peripheral Neuropathy: These are two of the commonest conditions that cause secondary RLS. Iron-deficiency anaemia (low blood) is caused due to haemoglobin deficiency (the substance in red blood cells that transports oxygen to different cells and tissues of the body). Peripheral neuropathy is a condition in which the nerves of the arms and legs are damaged. Peripheral neuropathy can be caused due to several medical conditions. Diabetes is one of the commonest causes of peripheral neuropathy. People with peripheral neuropathy complaint of numbness or lack of sensation, tingling, and pain in the affected areas.
- Pregnancy: Symptoms of RLS can be observed in about 40% of pregnant women. However, in most women, the symptoms disappear within a few weeks of delivery.
- Kidney failure: People with kidney failure can develop RLS due to iron deficiency, anaemia or the build-up of toxins in the body (uraemia).
- Medications: Several medications such as anticonvulsant drugs (e.g., methsuximide, phenytoin), anti-depressant drugs (e.g., amitriptyline, paroxetine), beta-blockers, H2 blockers, lithium, and neuroleptics (antipsychotics) may cause RLS.
- Cigarette smoking, alcohol, caffeine, may cause or worsen symptoms of RLS.
- Some other secondary conditions which can cause symptoms of RLS include magnesium deficiency, vitamin B-12 deficiency, severe kidney disease, amyloidosis, Lyme disease, rheumatoid arthritis, and Sjogren syndrome.