Patients undergoing dialysis therapy due to end-stage renal disease (ESRD) present a high prevalence of sleep disorders, including restless legs syndrome (RLS). However, the known data generally have been obtained from relatively small patient samples, coming from single or very few dialysis units. Moreover, some data were collected prior to the recent improvements in dialysis techniques, pharmacological therapies and to the establishment of internationally recognised diagnostic criteria for RLS. In order to study the incidence of the different sleep disorders, and of RLS in particular, in a large population of dialysis patients, a questionnaire was administered to all the patients in dialysis units of the 'Triveneto' area (Italy) who agreed to participate. The first part of the questionnaire included questions about demographic data, general medical history, history of renal disease, dialytic treatment and pharmacological therapy. The second part, which was self-administered, explored the patient's complaints about sleep, the presence of the minimal International Restless Legs Syndrome Study Group (IRLSSG) criteria for the diagnosis of RLS, the Epworth Sleepiness Scale and questions particularly related to somnolence. Patients whose responses indicated a diagnosis of RLS according to the IRLSSG criteria were requested to answer the 10 questions of the IRLSSG Severity Scale. The same group of patients was compared to those who did not fulfil any of the four minimal criteria for RLS. Statistical analysis was performed by using ANOVA and non-parametric tests. Whenever possible, data were compared with the database of the Veneto Dialysis Register. The first 601 consecutive questionnaires that we were able to analyse are presented in this paper. Applying the IRLSSG criteria for the diagnosis, the percentage of RLS patients in our sample was 21.5%, with a score of 20.5+/-8.7 on the IRLSSG Severity Scale. Comparing patients who are definitely affected by RLS (n=127) with unaffected patients (n=280), we found that the two groups did not differ as to age, sex, weight, body mass index (BMI), and intake of nicotine, alcohol and caffeine. Similarly, the two groups did not differ as to the etiology of ESRD, type of dialysis or percentage of previous transplantations; however, the period of dialysis dependence was significantly lower in the group negative for RLS. The use of drugs did not differ in the two groups, except for lower intake of phosphorus binders and antihypertensive drugs among RLS patients. No patient was receiving specific treatment for RLS. RLS patients reported more fragmented, less restful nightly sleep and more daytime somnolence, more often presented symptoms of other sleep disorders and were more affected by anxiety or depression. The high prevalence of RLS and other sleep disorders among uremics requires careful investigation of nocturnal sleep; although often underdiagnosed, correct identification of these disorders can lead to better therapy and improvement of clinical conditions and quality of life. Sleep fragmentation and sleep deprivation caused by RLS may contribute to the cardiovascular complications and infections, often with bad prognosis in dialysis patients.
