Experts believe that more people have restless leg syndrome than the official tally, but the question is how many more? The estimate from the National Institutes of Health puts the number at about 12 million Americans.

However, restless leg syndrome (RLS) is difficult to diagnose, and a study from Germany may indicate that vastly more people have the condition than previously believed. The study found that although restless leg was common in the German population, it was extremely underdiagnosed.

Restless leg syndrome robs sufferers of much-needed rest as they try to relieve the discomfort by constantly shifting and moving.

Restless leg syndrome is a disorder in which people keep moving their legs to alleviate discomfort. People with restless legs describe sensations with many adjectives: tingling, burning, crawling, itching, painful or pulling. Some describe the sensation as if insects are crawling inside their legs. These feelings are not the same as soreness or muscle fatigue. The sensations also may occur in the arm or trunk.

Although sensations can and do occur during the day, they are most active at night when a person is trying to sleep or has just fallen asleep. Restless leg syndrome robs sufferers of much-needed rest as they try to relieve the discomfort by constantly shifting and moving. Daytime fatigue is a hallmark of the syndrome.

Numerous studies have linked lack of sleep - from all causes - to serious health and emotional problems. Poor sleep contributes to car and on-the-job accidents, and has been linked to obesity, heart disease, stroke and other health issues. The importance of sleep has prompted some doctors to urge that sleep assessments be made a standard part of medical care.

So why is restless leg syndrome so hard to diagnose? Currently, there is no way to definitively identify the condition, so doctors must rely on a patient's description of symptoms, their sleep habits, their medical history and other subjective information.

Tests including blood tests, ultrasound, nerve conduction tests and others may be performed to rule out other causes. For instance, iron deficiency, has been linked to restless legs. Diabetes and kidney problems also are culprits. When caused by some other disorder, restless leg syndrome is classified as a secondary condition.

However, the majority of cases are primary, and doctors are not sure why the syndrome occurs. Considered a neurological problem, it is believed to involve a neurotransmitter called dopamine. Dopamine transmits signals in parts of the brain that control muscle movement. Stress may also play a role, as symptoms worsen during stressful periods.

In addition, some people do not seek medical attention, believing their symptoms are not serious enough or cannot be treated. Misdiagnosis is also common, because the symptoms can be easily attributed to other causes, such as arthritis or muscle cramps.

A diagnosis of restless leg syndrome includes the following criteria.

• An almost irresistible urge to move the leg with sensations as described above. Symptoms begin or grow worse during rest.
• Temporary relief from these sensations during movement. Relief lasts only as long as you are moving.
• Symptoms are worse in the evening, especially when you are lying down.

Larger studies are underway to determine the extent of restless leg syndrome. If you believe you may have restless leg syndrome, keeping a close record of your symptoms will help your doctor in the diagnosis. Although there is no cure, medical therapies can help reduce symptoms and improve sleep. The syndrome may also go into remission, in which symptoms decrease or disappear for weeks or months at a time.