Clinical Review
Epidemiology of restless legs syndrome: The current status

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Summary

Epidemiological studies in restless legs syndrome (RLS) have often been limited by misdiagnosis and by the fact that affected individuals, even when their symptoms are severe, might not seek medical care. Some of these limitations have been overcome in the last years as population studies based on face to face interviews have been carried out with new standardized diagnostic criteria. According to these studies, and in contrast to earlier views, RLS has been shown to be a common disorder with prevalences ranging between 2.5 and 10% of the population. Although few studies performed outside Europe/North America have shown a low prevalence, a number of methodological issues have been raised that might question these results.

Furthermore, once established, RLS usually follows a chronic course, and preliminary evidence shows that it might worsen over time in some patients. Endstage renal disease, increasing age, female gender, pregnancy, frequent blood donations, iron deficiency and neuropathy are considered to be risk factors for this disorder. The association to RLS is less definitely established for other conditions, such as PD or diabetes.

In summary, epidemiological evidence suggests that RLS is a common neurological disorder—with high impact on many aspects of the life of those affected.

Introduction

Epidemiological studies of restless legs syndrome (RLS) have often been limited by two main factors: on the one hand, subjects suffering from RLS frequently do not seek medical care, even when their symptoms are severe. For studies based on outpatients or clinical patient populations this selection could lead to an underassessment of cases. Second, RLS is a frequently misdiagnosed disorder: due to their sensory-motor manifestations, RLS can often be attributed to insomnia, stress, muscle cramps, arthritis, aging, or even psychological disorders. Thus, epidemiological studies were often limited in the past by poor recognition and misclassification.

Accordingly, RLS has been believed to be a rare disorder for a long time. Poor recognition, absence of symptoms during most of the day (with an onset just at night), along with a frequently ‘bizarre’ description of symptoms, often led to the consideration of a psychogenic origin of these symptoms. The absence of any classical objective findings such as nerve conduction studies, electromyography, etc. further contributed to this consideration. As a result, a lack of interest by neurologist and the entire medical profession towards RLS has existed historically.

However, over the last years, RLS has emerged not only as a common, but also as a frequently severe, disorder.80, 81 Major advances have been achieved in terms of diagnostic classification, epidemiology, pathophysiology, and therapy. Moreover, the fact that RLS can be a common neurological disorder, together with its chronic course, and the frequently genetic origin, has undoubtedly contributed to the recent surge in attention on this disorder.

Section snippets

RLS in the general and primary care populations

Although the first description of RLS has usually been attributed to T. Willis,1 RLS was not understood as a common disorder until it was described by the Swedish neurologist Ekbom.2 In a first estimation in a sample of patients in his neurological practice, he suggested a 5% prevalence.

Such an estimation, suggesting that RLS might in fact be a common disorder, was confirmed by the studies that followed. Most of these prevalence studies have been performed over the last twenty years (Table 1a).

Restless legs syndrome in non-western populations

The number of studies conducted outside Europe/North America that assessed the prevalence of RLS in the population is very small. Nevertheless, they have received considerable attention because the prevalences observed were very low compared to Caucasian populations.

The question raised was whether restless legs syndrome was particularly rare in Asia. Only three studies related to Asian general populations have been published so far. One of them22 did not apply the four minimal criteria and used

RLS in the elderly

Age belongs to the group of factors, such as gender, ethnicity or genetic susceptibility, that cannot be targeted by behavioral changes. Increasing age would thus be an important determinant for the number of affected patients in a given population. In this context, it is well-known that many diseases, especially neurological conditions, are age related. The number of studies that evaluated age effects for the occurrence of RLS and applied the minimal criteria on a population level for RLS

The question of gender

Many studies have observed a higher prevalence for RLS in women than in men. Specifically, those studies performed after the minimal criteria were introduced in 1995 found that women were affected with RLS approximately twice as often as men. This gender effect was observed regardless of the absolute level of RLS prevalence in the respective population. This agrees with early clinical observations suggesting that RLS patients were more often female and that RLS was frequently observed in women

RLS in pediatric populations

Some studies have tried to assess the prevalence of RLS in children. Thus, Chervin et al.31 evaluated 866 children between 2 and 13.9 years diagnosed as having attention deficit disorder and found that 17% fulfilled criteria for pediatric RLS. Similarly, Rajaram et al. showed that 10 out of 11 children with growing pains (mean age 10.4 years) fulfilled criteria for RLS.32 Furthermore, in individuals affected by familial forms of RLS, symptoms may have already been initiated during childhood.4,

Long term course of RLS

A retrospective analysis of the long term course shows that RLS patients will generally suffer from symptoms for many years and experience a worsening of these over time.35, 36 Furthermore, as shown above, the prevalence of idiopathic RLS increases with advancing age, which is consistent both with its chronic course and the fact that symptoms become more prominent over time.

Prevalence of RLS in secondary forms and associated conditions

Since, the initial description of the disorder, it has been known that RLS can be associated with a variety of conditions including metabolic and hormonal alterations, pregnancy, neuropathies37, 38 and spinal/brainstem lesions within the central nervous system.39, 40 However, only a few studies that used the full diagnostic criteria investigated the prevalence of RLS in these populations. In order to show a real association, the studies should show a significant increase in the prevalence of

Conclusions

RLS has emerged out of the previously discussed prevalence studies as one of the main sleep and neurological disorders. The definition of the four minimal criteria in 1995 has been followed by an increasing number of studies that examined frequencies, risk factors and consequences of restless legs syndrome in the general population. However, compared to the number of studies conducted in RLS patients, the number of general population studies is still small.

The application of the four minimal

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