This disorder was seldom investigated in the general population. Prior to our study, existing figures for RLS were estimated using a limited set of questions that could have inflated the prevalence of the disorder, which was found to be around 10% (Lavigne and Montplaisir, 1994; Phillips et al., 2000).

RESTLESS LEGS SYNDROME AND ITS SYMPTOMS

Patients with RLS mostly complain of itching, creeping, tingling in their legs mostly between the ankle and the knee. These unpleasant sensations occur when the subject is at rest and are more pronounced in the evening or at night. The unpleasant sensations are relieved temporarily with leg movements.

DIAGNOSIS OF RLS

The diagnosis of RLS is based primarily on the subject's history. The International RLS study group (Walters, 1995; Allen et al., 2003 for the revised criteria) proposed the following 4 essential criteria for the diagnosis of RLS:

• An urge to move the legs usually accompanied or caused by uncomfortable and unpleasant sensations in the legs;
• The urge or unpleasant sensations begin or worsen during periods of rest or inactivity
• Symptoms are partially or totally relieved by movement; and
• Symptoms are worse in the evening or at night than during the day or are present only at night or in the evening.

RLS may begin at any age but most patients suffering of RLS are over age 40. About 40% of patients diagnosed with RLS during adulthood reported having experienced symptoms before the age of 20 years. Some studies reported that as many as 80% of RLS sufferers have also PLMS (Montplaisir et al., 1997).

ETIOLOGY OF RLS

The etiology of RLS is not well known but several pathophysiological mechanisms were proposed:

• RLS has been also linked with lower serum ferritin levels. Up to 31% of RLS older-age patients would have iron deficiency (O'Keeffe et al., 1993). Oral iron supplements therapy produced significant reduction in RLS symptoms (O'Keeffe et al., 1994) but this was not confirmed in another study (Davis et al., 2000). Relationship between RLS and iron deficiency was not supported in uremic patients with or without RLS (Collado-Seidel et al., 1998). However, results of recent researches showed that idiopathic RLS patients with normal serum ferritin levels have a 65% reduction in CSF ferritin and an increase in CSF transferrin (Earley et al., 2000). Therefore, brain iron storage may be reduced in idiopathic RLS patients.
• Uremia is another possible cause for RLS (Callaghan, 1966). In a study on 136 uremic patients, 23% of them were found with RLS (Collado-Seidel et al., 1998). Similarly, uremia was found to be the cause of RLS in 22.3% of 300 RLS patients (Winkelmann et al., 2000).
• Other factors have also be identified to cause RLS: folate deficiency, vascular insufficiency (Harvey, 1976), chronic obstructive pulmonary disease (Spillane, 1970), gastroctomy (Banerji et al., 1970), diabetes mellitus (Skomro et al., 2000; Phillips et al., 2000) and caffeine abuse (Lutz, 1978).

PREVALENCE OF RLS IN THE GENERAL POPULATION

Table 1. Prevalence for restless leg syndrome or symptoms

IRLSSG = International Restless legs Syndrome Study Group
ICSD = International Classification of Sleep Disorders

Authors	Place	N	Age	Criteria	Prevalence	Comments
Lavigne & Montplaisir (1994)	Canada	2,019	≥ 18	None	10.0%	Household interviews, prevalence based on a single question
Phillips et al. (2000)	Kentucky, USA	1,803	≥ 18	None	9.4%	Telephone interviews, prevalence based on a single question
Rothdach et al. (2000)	Augsburg, Germany	385	65-83	IRLSSG	9.8%	Face-to-face interview, 3 questions based on criteria described by the International RLS Study group (need positive answers to all questions)
Ulfberg et al. (2000)	Sweden	2,608 men	18-64	IRLSSG	5.8%	Postal questionnaire, 4 questions based on criteria described by the International RLS Study group (need positive answers to all questions)
Ohayon and Roth (2002)	5 European countries	18,980	15-100	ICSD	5.5%	Telephone interviews, prevalence based on ICSD criteria evaluated by an expert system
Sevim et al (2003)	Mersin, Turkey	3,234	≥ 18	IRLSSG	3.2%	Face-to-face interview, 4 questions based on criteria described by the International RLS Study group (need positive answers to all questions) + the IRLSSG severity scale
Berger et al. (2004)	Pomerania, Germany	2,019	≥ 18	IRLSSG	10.0%	Face-to-face interview, 3 questions based on criteria described by the International RLS Study group (need positive answers to all questions)

Existing figures for RLS were estimated using a limited set of questions (one or two questions).

• The prevalence of RLS symptoms was found to be around 10% (Lavigne & Montplaisir, 1994; Phillips et al., 2000).
• Three European studies used set of criteria to assess the prevalence of RLS in the general population. - One was done only with men (Ulfberg et al., 2000), another was conducted with elderly (Rothdach et al., 2000) - The other was performed with subjects 15 years of age or over (Ohayon and Roth, 2002). The Rothdach's study (2000) with elderly people found a prevalence of 9.8%. Ohayon and Roth in the same age group, found a prevalence of 8.6%. The Swedish men study (Ulfberg et al., 2000) reported a prevalence of 5.8%. Ohayon and Roth found a prevalence of 5.4% in the men of their sample.

In two studies, RLS was not gender related (Phillips et al., 2000; Ohayon and Roth, 2002) and in four other the prevalence of RLS was about two times higher in women than in men (Lavigne & Montplaisir, 1994; Rothdach et al., 2000; Sevim et al , 2003; Berger et al. 2004).

Five studies showed that RLS increased with age (Lavigne & Montplaisir, 1994; Phillips et al., 2000; Ohayon and Roth, 2002; Sevim et al , 2003; Berger et al. 2004). The prevalence of RLS symptoms is close to 20% in elderly people and around 5% for subjects younger than age 30 (Lavigne & Montplaisir, 1994; Phillips et al., 2000).

In the Ohayon study, prevalence of RLS diagnosis ranged from 2.7% in the 15-18 year old group to 8.3% in the group of subjects aged 60 and over (60-69: 8.3%; 70-79: 8.7%; >= 80: 8.2%).

THE SLEEP-EVAL RESEARCH

Cross-sectional studies were performed in the United Kingdom, Germany, Italy, Portugal and Spain. Overall, 18,980 subjects aged 15 to 100 years old representative of the general population of these five European countries underwent telephone interviews with the Sleep-EVAL system. A section of the questionnaire assessed leg symptoms during sleep. The diagnosis of RLS was based on the minimal criteria provided by the International Classification of Sleep Disorders. It was analyzed in association with physical and mental health status and the use of psycho-active substances (alcohol, coffee, tobacco, CNS medications) that could explain the disorders.

RESULTS

Overall:

• 3.2% of sample reported to have several nights per month unpleasant feelings in their legs at the moment of going to sleep; 6.4% have these feeling several nights per week and 0.9% have them on a nightly basis.
• Leg pain during sleep occurred:
• several nights per month in 4.9% of the sample;
• 9.5% said they have leg pain several nights per week and
• 1.0% said they have this pain on a nightly basis.

When combining all the questions related to these leg symptoms, we found that 12.7% of the sample have whether unpleasant sensations in legs or feeling of creeping or shivering in their calves at sleep onset at least several nights per month. Leg pain occurring at least several nights per month was found in 15.5% of the sample and legs movements occurring at least several nights per month were found in 23.9% of the sample. The co-occurrence of these symptoms was frequent: 3.9% of the sample reported the three leg symptoms; 9.0% reported at least two symptoms and 22.0% reported only one leg symptom.

Subjects meeting ICSD minimal criteria for RLS represented 5.5% of the sample (0.5% were excluded because other causes could have explained the unpleasant feelings in the legs). This prevalence was comparable between men and women but it significantly increased with age.

In multivariate models, were significantly associated:

• being a woman,
• the presence of musculo-skeletal disease,
• heart disease,
• obstructive sleep apnea syndrome,
• cataplexy,
• doing physical activities close to bedtime and the presence of a mental disorder,
• advanced age,
• obesity,
• hypertension,
• loud snoring,
• drinking at least 3 alcoholic beverages per day,
• smoking more than 20 cigarettes per day and
• use of SSRI.

This condition is associated with several physical and mental disorders and may negatively impact sleep.

Greater recognition of these sleep disorders is needed.

REFERENCES

1. Ohayon MM. Epidemiology of sleep disorders in the general population. Guilleminault C (ed) Sleep and its disorders. Series Handbook of Clinical Neurophysiology, 2005
2. Ohayon MM, Roth T. Prevalence of restless legs syndrome and periodic limb movement disorder in the general population. J Psychosom Res 2002; 53:547-554.