Sleep Medicine
Volume 11, Issue 1 , Pages 82-86, January 2010

Epidemiology of restless legs syndrome in Turkish adults on the western Black Sea coast of Turkey: A door-to-door study in a rural area

  • Mustafa Taşdemir

      Affiliations

    • School of Medicine, Marmara University, 34668 Haydarpaşa, Istanbul, Turkey
    • Corresponding Author InformationCorresponding author. Address: Marmara Üniversitesi Tıp Fakültesi, Halk Sağlığı Anabilim Dalı, 34668 Haydarpaşa, İstanbul, Turkey. Tel.: +90 216 414 9457; fax: +90 216 414 4731.
    • Dr. Taşdemir recently transferred from School of Health Sciences to School of Medicine of Marmara University.
    • ,
  • Hülya Erdoğan

      Affiliations

    • Department of Neurology, Dr. Lütfi Kırdar Kartal Training and Research Hospital, 34865 Kartal, Istanbul, Turkey
    • ,
  • Ülkü Türk Börü

      Affiliations

    • Department of Neurology, Dr. Lütfi Kırdar Kartal Training and Research Hospital, 34865 Kartal, Istanbul, Turkey
    • ,
  • Elif Dilaver

      Affiliations

    • Department of Neurology, Dr. Lütfi Kırdar Kartal Training and Research Hospital, 34865 Kartal, Istanbul, Turkey
    • ,
  • Ayşegül Kumaş

      Affiliations

    • Department of Neurology, Dr. Lütfi Kırdar Kartal Training and Research Hospital, 34865 Kartal, Istanbul, Turkey

Received 12 March 2008; received in revised form 6 October 2008; accepted 7 October 2008.

Article Outline

Abstract 

Objective

To determine the prevalence and clinical presentation of restless legs syndrome (RLS) in Turkish population living in Kandıra, a town located on the Black Sea coast of Istanbul.

Methods

This study was designed as a descriptive, cross-sectional, door-to-door field study. A total of 2111 people aged 18 years and over were selected for the study. The criteria suggested by the IRLSSG (International Restless Legs Syndrome Study Group) were used in the assessment of RLS. All the suspected subjects underwent neurological examination.

Results

The prevalence of RLS was found to be 3.4% of Turkish population aged over 18. Female:male ratio was 3.5:1. The prevalence reached peak point (8.3%) in the 58- to 67-year-old group. Prevalence of DM, anemia and polyneuropathy in RLS patients was 13.9%, 8.3% and 4.2%, respectively.

Conclusion

RLS prevalence is relatively low, but increases with age in both genders in this Turkish population. Although it has negative effects on daily life, it is not well recognized by the population.

Keywords: Restless legs syndrome, Prevalence, Turkey, Severity, Co-morbidity, Rural

 

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1. Introduction 

Restless legs syndrome (RLS) is a sensorimotor disturbance that may cause profound sleep disorders. It is characterized by distressing deep sensations in the limbs, particularly the legs, associated with an urge to move often at bedtime [1], [2]. It was first described by Ekbom in 1945 [3]. The number of epidemiological studies has rapidly increased after the International Study Group declared the diagnostic criteria [1]. Prevalence of RLS shows variation from country to country. Population-based studies using the full standard diagnostic criteria for RLS report a prevalence of 5–10% [4], [5], [6] in Western countries, but a lower prevalence in Asian populations [7], [8].

There is only one field study evaluating RLS in Turkey which is limited to the Mediterranean region. We carried out this study to assess the prevalence of RLS in a rural setting on the western Black Sea coast of Turkey.

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2. Methods 

This study is a part of two large neuroepidemiology projects performed jointly by Kartal Dr. Lütfü Kırdar Training and Research Hospital and Marmara University School of Health Sciences.

2.1. Study region 

Kandıra is a town located at the north of Izmit Bay on the Black Sea coast (Fig. 1). Its overall population is 50,214 and the city center population is 12,641. There are four neighborhoods in the central town which are similar geographically, socioeconomically and demographically. The town has rural characteristics. Eighty percent of the population farm. There is not any major industrial facility. The people are of low or middle socioeconomic class.

2.2. Population 

The population is almost homogenously Turkish. Immigration to and from Kandıra is very limited. The ratio of young population is relatively high.

2.3. Sampling method 

The prevalence of the disease was accepted as 5% based on Turkish literature and the sample size was determined (using GraphPad Instat Software [GraphPad Instat Software Inc., San Diego, CA, USA]) as 2000 under the following conditions: minimum difference detected as significant was 0.02, alpha error as 0.05 and the power of the study was 80%.

The four neighborhoods were taken as strata. From each neighborhood 500 persons were taken into the sample. These 500 people were selected randomly with the “quota sampling and random walk” method [9]. The number 500 was the quota. We randomly selected the first household in each neighborhood and then walked through the streets successively. We visited every available household until the quota was reached.

2.4. Questionnaire 

A form including the demographic features consisting of 10 items was administered to each person included in the study. The Turkish version of four minimal criteria suggested by the IRLSSG (International Restless Legs Syndrome Study Group) was used in the assessment for RLS: (1) the desire to move the limbs associated with paresthesias/dysesthesias, (2) motor restlessness, (3) symptoms worse or present exclusively at rest (i.e., lying or sitting) with at least partial or temporary relief by activity and (4) symptoms worse in the evening or at night. If it was necessary, the four screening questions were explained in detail to participants. In addition to the four minimal criteria, the following were asked: co-morbidities (diabetes mellitus, kidney disease, vitamin B12 deficiency, Parkinson’s disease, rheumatoid arthritis, anemia, polyneuropathy and pregnancy) and if family members, spouses and close relatives had RLS symptoms. Since we had many female patients insisting that their husbands had RLS symptoms, we added a question about this to the questionnaire. The second part of the questionnaire consisted of the 10-item IRLSSG Rating Scale (IRLS) which was used to assess the severity of RLS [10].

The Turkish versions of both the four minimal criteria and IRLS were formerly found to be reliable [11].

2.5. Data collection 

The epidemiologic survey consisted of “face-to-face, door-to-door” interviews with 2111 adult residents of Kandıra. All the interviews were conducted in April 2006 by three neurology residents (one of whom is senior). Every member of the household visited was interviewed. The interviewers performed thorough neurological examinations for differential diagnosis of RLS and for exploring any co-morbidity of those respondents who fulfilled RLS criteria in order to eliminate interobserver variability. Any case evaluated as suspicious by the clinician was examined by the chief conductor neurologist; cases were diagnosed unanimously by both physicians. Then, RLS-diagnosed patients were administered the second part of the questionnaire, the IRLS.

DM, anemia, chronic renal disease and polyneuropathy were reported by patients, but only those diagnosed by a physician were recorded as cases.

2.6. Statistical analysis 

Statistical analysis was performed using SPSS software, version 11.05. For categorical variables, the data were summarized with frequency and contingency tables. For continuous variables, data were presented as means±SD unless otherwise specified. The prevalence rates by gender and 10-year age groups from 18 to >67 years were calculated. The subjects diagnosed as RLS were divided into four groups with respect to the severity of symptoms according to IRLS score (mild: 0–10, moderate: 11–20, severe: 21–30, very severe: 31–40). The distribution of subjects among these four groups with respect to gender and age group was calculated. Comparisons were made using the chi-square test for categorical variables and t-test for continuous ones. p values <0.05 were statistically significant.

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3. Results 

Thanks to the accompanying nurses working for local health authority and visiting households routinely, thus having close relationships with the people, we encountered no refusal. The ratio of unavailable households was about 7% (n=134), thus the rate of participation was 93%.

The age and gender distributions of the study sample were more or less similar to those of the population of Mersin and the population of Turkey >19 years of age (Fig. 2). Unfortunately we could include the >19 age group instead of the >17 age group because of lack of appropriate data.

Of 2111 subjects, 1104 (52,3%) were female and 1007 (47,7%) were male. Mean age of women was 38.35±15.46 years and that of men was 38.78±15.38 years.

Seventy-two subjects were diagnosed with RLS, thus the prevalence of RLS was found to be 3.4%. Prevalence in females (n=56) was 5.1%, in males (n=16) 1.6% (p<0.001). Female:male ratio was 3.5:1.

RLS prevalence in the 18–27 age group was 1.4%. Peak point (8.3%) was reached at 58–67 years. Prevalence decreases after the age of 67 in both males and females (Fig. 3).

3.1. Co-morbidities 

Prevalence of DM, anemia and polyneuropathy in RLS patients was 13.9%, 8.3% and 4.2%, respectively. Prevalence of these diseases in RLS patients was found to be significantly higher than those who do not have RLS. For others (renal disease, vitamin B12 deficiency, Parkinson’s disease, rheumatoid arthritis and pregnancy); the difference in prevalence was not statistically significant (Table 1).

Table 1. Prevalence of co-morbidities in RLS patients and those without RLS.
DiseasePrevalencep
RLSNot RLSTotal
DM (n=61)13.92.52.9<0.001
Renal disease (n=9)1.40.40.40.269
Vit. B12 deficiency (n=3)–0.10.10.901
Parkinson’s disease (n=3)–0.10.11.000
Rheumatoid arthritis (n=9)1.40.40.40.269
Anemia (n=29)8.31.11.4<0.001
Polyneuropathy (n=15)4.20.60.70.013
Pregnancy (n=9)1.40.40.40.269

Polyneuropathy was reported in 20% of diabetic RLS patients and in 1.6% of non-diabetic RLS patients. The difference was again statistically significant (p=0.049).

3.2. Family history 

RLS symptoms were reported by any family member or close relative in 22.2% of RLS patients and in 15.3% of first-degree relatives (parents, siblings, children). The prevalence of RLS symptoms in first-degree relatives of those not having RLS was 0.4%. The difference was statistically significant (p<0.001).

3.3. Severity 

Of those diagnosed with RLS, 2.8% had mild symptoms, 52.8% had moderate symptoms and 44.4% had severe symptoms.

Restlessness affected daily activities in 93.1% and mood in 72.2% of those diagnosed with RLS. A sleep disorder was present in 94.4% of them, and 97.2% had daytime tiredness (Table 2). Only three of those diagnosed with RLS in this study had a previous diagnosis of RLS and were taking medication.

Table 2. Severity of symptoms (percentages of patients at severity levels).
IRLS itemSeverity (%)Totalb (excl. 0)
0a1234
Restlessness–15.343.134.76.9100.0
Urge to move–16.738.937.56.9100.0
Relief by activity–26.425.018.030.6100.0
Sleep disorder5.631.943.118.01.494.4
Sleeplessness and tiredness2.836.138.922.2–97.2
All complaints–18.041.738.91.4100.0
Frequency of restlessness–13.948.619.418.1100.0
Duration of restlessness–25.062.511.11.4100.0
Restlessness affecting daily activities6.951.436.15.6–93.1
Restlessness affecting mood27.843.026.42.8–72.2

aNo symptom.

bTotal percentage of those having symptom.

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4. Discussion 

The prevalence of RLS was found to be 3.4% in a Turkish population screened according to the criteria of IRLS. This result is similar to that (3.19%) found in the Mediterranean coast of Turkey. That study used the same criteria and similar methodology [11]. Our study was conducted on the Black Sea coast which is in the northern part of Turkey, whereas the other study was in the southern part. There is a latitude difference of 6° between these two regions, thus the difference in climate and geographic structure. These factors seem to have no significant effect on the prevalence of RLS.

In recent population-based studies with published data on the prevalence and associated characteristics of RLS [5], [6], [7], [8], [9], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25] some used IRLS criteria [5], [6], [8], [11], [13], [16], [18], [20], [21], [22], [23], [24]. The population-based direct interview survey in the elderly (65–83 years of age) conducted in Germany reported a prevalence of 9.8% [13]. The Canadian study (not based on IRLS criteria) interviews found that 10% of the community reported “unpleasant leg muscle sensations” associated with awakening during sleep and with the irresistible need to move or walk [12]. Such RLS-related symptoms were reported more frequently in Eastern provinces than in Ontario and Western Canada [16], [23].

The REST general population study was conducted in the United States and five European countries (France, Germany, Italy, Spain and the United Kingdom). The REST study found the prevalence in those above age 18 to be 7.2%, and the prevalence in females was two times that of males. There was no difference in prevalence between Europe and the US, but prevalence in France was significantly higher [24]. A recent study in France disclosed a prevalence of 8.5% in the adult population [18]. A more recent study in Italy found the prevalence to be 8.9% [16]. A Holland study with mailed questionnaires found a prevalence of 7.2% in an above 50 age group [22].

In Asia, a study in Singapore found a very low estimated prevalence of RLS: less than 1% [8]. A recent study in Japan revealed prevalence in an above 65 age group as 4.6% [20]. In a more recent Korean study, prevalence in a 40–69 age group was found to be 12.1% [17].

There is a significant variation between the figures of Asian countries. The Japanese figure is similar to ours, but the Korean figure is much higher. Our results are also much lower than those of European and North American countries, but higher than that of Singapore.

This variation in results shows the impact of the population on RLS prevalence. The variation in results of different countries may result from differences in age structure and racial/genetic characteristics and methodologies used. However, prevalences in Western countries are usually higher than those in Asian countries.

Most studies found the prevalence in females to be two times that in males [5], [6], [13], [14], [18]. We found the ratio to be 3.5:1. There is a clear female predominance in most studies.

We found that RLS prevalence increases with age. In many studies, it was shown that prevalence increases with age and reaches its peak at 45–54 years [4], [26], [27], [28]. We observed the highest rate in the 58–67 age group, with a decrease after age 67.

In this study, the most severely affected were older women. In the great majority of patients, symptoms affected daily life and mood badly. This is in line with other studies [4], [8], [11], [12], [35]. Only this result is sufficient to point out the importance of diagnosis and treatment of RLS.

RLS symptoms were reported in first-degree relatives of 15.3% of RLS patients in our study. This figure is lower than those of previous studies [2], [16], [19], [29], [30]. In this study, many people became aware of their illness upon our inquiry. Those people might not have noticed the others’ symptoms. There are some studies that suggest genetic factors affect RLS prevalence [31], [32], [33], [34].

Another important finding in our study is that very few people were aware of their disease and visited a physician. This ignorance may result from not seeing it as a disease, and, in turn, may explain the low rate in family history records. In the UK, patient records revealed a prevalence of 0.25% [35]. This shows that even in developed countries neither doctors nor people recognize the disease.

It was surprising that the RLS patients in our study reported a significantly high prevalence of RLS symptoms in their spouses (8.3% in spouses of RLS patients; none in spouses of others, p=0.000). In fact, it is very difficult to present or find out scientific evidence to explain this significance. Maybe an old Turkish saying, “If you sleep with a blind man you will wake up crosseyed,” can inspire an explanation for it.

We found the prevalence of DM in RLS patients to be higher compared to some other studies [11], [35]. This might result from the fact that we did not diagnose DM; instead we asked the RLS patients if they had pre-diagnosed DM. This point may be a source of bias in our study. Twenty percent of these patients also had polyneuropathy. A very recent study found a high prevalence of RLS in Type 2 DM patients [36]. RLS may result from polyneuropathy in diabetic patients.

The frequency of anemia was found to be lower than expected in our study. This may result from our methodology. We got the data from patients’ responses and did not conduct any blood analysis. If we had done a laboratory analysis, the frequency of anemia may have been higher. The frequencies of rheumatoid arthritis and pregnancy were also quite low in our study.

The finding that the prevalence of RLS in the most northern part of Turkey is almost equal to that found in the most southern part has shown that this figure reflects the prevalence of the Turkish population.

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Acknowledgements 

We would like to thank Mr. Mehmet Sarıcan, Head Official of the District; Dr. Savaş Öz, Head of the District Health Authority; and the nurses for their support in this research.

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References 

  1. Walters AS The International Restless Legs Syndrome Study Group. Toward a better definition of the restless legs syndrome. Mov Disord. 1995;10:634–642
  2. Allen RP, Picchietti D, Hening WA. Restless legs syndrome: diagnostic criteria, special considerations, and epidemiology. A report from the restless legs syndrome diagnosis and epidemiology workshop at the National Institutes of Health. Sleep Med. 2003;4:101–119
  3. Ekbom KA. Restless legs. Acta Med Scand. 1945;(Suppl. 158):1–122
  4. Berger K, Luedemann J, Trenkwalder C, Ulrich J, Kessler C. Sex and the risk of restless legs syndrome in the general population. Arch Intern Med. 2004;164:196–202
  5. Ulfberg J, Nystrom B, Carter N, Edling C. Restless legs syndrome among working-aged women. Eur Neurol. 2001;46:17–19
  6. Ulfberg J, Nystrom B, Carter N, Edling C. Prevalence of restless legs syndrome among men aged 18 to 64 years: an association with somatic disease and neuropsychiatric symptoms. Mov Disord. 2001;16:1159–1163
  7. Tachibana N, Tanigawa T. Prevalance and clinical characteristics of restless legs syndrome among Japanese industrial workers. Neurology. 2003;60(Suppl. 1):A38
  8. Tan EK, Seah A, See SJ, Lim E, Wong MC. Restless legs syndrome in an Asian population: a study in Singapore. Mov Disord. 2001;16:577–578
  9. United Nations Department of Economic and Social Affairs Statistics Division. Designing household survey samples: practical guidelines. New York; 2005.
  10. The International Restless Legs Syndrome Study Group. Validation of the International Restless Legs Syndrome Study Group rating scale for restless legs syndrome. Sleep Med 4 (2003) 121–132.
  11. Sevim S, Dogu O, Camdeviren H. Unexpectedly low prevalence and unusual characteristics of RLS in Mersin, Turkey. Neurology. 2003;61:1562–1569
  12. Lavigne GJ, Montplaisir JY. Restless legs syndrome and sleep bruxism: prevalence and association among Canadians. Sleep. 1994;17:739–743
  13. Rothdach AJ, Trenkwalder C, Haberstock J, Keil U, Berger K. Prevalence and risk factors of RLS in an elderly population: the MEMO study. Memory and morbidity in Augsburg elderly. Neurology. 2000;54:1064–1068
  14. National Sleep Foundation. 2001 Omnibus sleep in America poll. Available from: http://www.sleepfoundation.org/publications/2001poll.cfm.
  15. Allen RP, La Buda MC, Becker P, Earley CJ. Family history study of the restless legs syndrome. Sleep Med. 2002;(Suppl 3):S3–S7
  16. Zucconi M, Ferini-Strambi L. Epidemiology and clinical findings of restless legs syndrome. Sleep Med. 2004;5:293–299
  17. Jinyoung K, Changho C, Kyungrim S, Hyeryeon Y, Mingyu P, Namhan C, et al. Prevalence of restless legs syndrome and associated factors in the Korean adult population: The Korean Health Genome Study. Psychiatry Clin Neurosci. 2005;59:350–353
  18. Tison F, Crochard A, Legér D, Bouée S, Lainey E, El Hasnaou A. Epidemiology of restless legs syndrome in French adults: a nationwide survey: the INSTANT study. Neurology. 2005;65:239–246
  19. Phillips B, Hennig W, Britz P, Mannino D. Prevalence and correlates of restless legs syndrome: results from the 2005 National Sleep Foundation Pool. Chest. 2006;129:76–80
  20. Mizuno S, Miyaoka T, Inagaki T, Horiguchi J. Prevalence of restless legs syndrome in non-institutionalized Japanese elderly. Psychiatry Clin Neurosci. 2005;59:461–465
  21. Högl B, Kiechl S, Willeit J, Saletu B, Frauscher B, Seppi K, et al. Restless legs syndrome: a community-based study of prevalence, severity, and risk factors. Neurology. 2005;64:1920–1924
  22. Rijsman R, Neven AK, Graffelman W, Kemp B, Weerd A. Epidemiology of restless legs in the Netherlands. Eur J Neurol. 2004;11:607–611
  23. Odin P, Mrowka M, Shing M. Restless legs syndrome. Eur J Neurol. 2002;(Suppl 3):59–67
  24. Hening W, Walters AS, Allen RP. Impact, diagnosis and treatment of restless legs syndrome (RLS) in a primary care population: the REST (RLS Epidemiology, Symptoms, and Treatment) primary care study. Sleep Med. 2004;5:237–246
  25. Vogl FD, Pichler I, Adel S, Pinggera GK, Bracco S, Grandi A, et al. Restless legs syndrome: epidemiological and clinicogenetic study in a South Tyrolean population isolate. Mov Disord. 2006;21:1189–1195
  26. Phillips B, Young T, Finn L, Asher K, Hening WA, Purvis C. Epidemiology of restless legs syndrome in adults. Arch Internal Med. 2000;160:2137–2141
  27. Odin P, Mrowka M, Shing M. Restless legs syndrome. Eur J Neurol. 2002;9(Suppl 3):59–67
  28. Hornyak M, Trenkwalder C. Restless legs syndrome and periodic limb movement disorder in the elderly. J Psychosom Res. 2004;56:543–548
  29. Winkelmann J, Wetter TC, Collado-Seidel V. Clinical characteristics and frequency of the hereditary restless legs syndrome in a population of 300 patients. Sleep. 2000;23:597–602
  30. Winkelmann J, Muller-Myhsok B, Wittchen HU. Complex segregation analysis of restless legs syndrome provides evidence for an autosomal dominant mode of inheritance in early age at onset families. Ann Neurol. 2002;52:297–302
  31. Bonati MT, Ferini-Strambi L, Aridon P, Oldani A, Zucconi M, Casari G. Autosomal dominant restless legs syndrome maps on chromosome 14q. Brain. 2003;126:1485–1492
  32. Brooks DG. The first genetic locus mapped for RLS is unlikely to be the last. [Article reviewed: “Identification of a major susceptibility locus for restless legs syndrome on chromosome 12q”] Sleep Med. 2002;3:285–286
  33. Ondo WG, Vuong KD, Wang Q. Restless legs syndrome in monozygotic twins: clinical correlates. Neurology. 2000;55:1404–1406
  34. Chen S, Ondo WG, Rao S, Li L, Chen Q, Wang Q. Genome-wide linkage scan identifies a novel susceptibility locus for restless legs syndrome on chromosome 9p. Am J Hum Genet. 2004;74:876–885
  35. van de Vijver DAMC, Walley T, Petri H. Epidemiology of restless legs syndrome as diagnosed in UK primary care. Sleep Med. 2004;5:435–440
  36. Lopes LA, Lins CMM, Adeodato VG, Quental DP, de Bruin PFC, Montenegro RM, et al. Restless legs syndrome and quality of sleep in type 2 diabetes. Diabetes Care. 2005;28:2633–2636

PII: S1389-9457(09)00061-6

doi:10.1016/j.sleep.2008.10.008

Sleep Medicine
Volume 11, Issue 1 , Pages 82-86, January 2010

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