Restless legs syndrome and leg cramps in fibromyalgia syndrome: a controlled study

Subjects, methods, and results

One hundred and thirty five consecutive new female patients referred with primary fibromyalgia, 54 women with rheumatoid arthritis without concomitant fibromyalgia, and 87 healthy, pain free women acting as controls were studied at our outpatient rheumatology clinic. All patients with fibromyalgia fulfilled the criteria of Yunus et al.4 No subjects had peripheral neuritis.

White cell count; haemoglobin concentration; erythrocyte sedimentation rate; serum calcium, electrolyte, blood urea nitrogen, creatinine, and liver enzyme values; and thyroid function were normal in the patients with fibromyalgia. Patients with rheumatoid arthritis had normal serum calcium, electrolyte, blood urea nitrogen, and creatinine values. Symptoms as well as tender points were evaluated by a questionnaire with ordinal grading (none, mild, moderate, severe). Global anxiety, depression, and mental stress were assessed by the following questions: “Do you think you are anxious or tense or have worries?,” “Do you feel depressed, low, and blue?,” and “Do you feel under mental stress?”

For statistical analysis symptoms were dichotomised (moderate or severe= yes; none or mild=no). When the sample was stratified by age (at the median), a Mantel-Haenszel χ² test was used to control for potential impact of age on leg symptoms. Analysis of variance was used for interval variables, followed by the Student-Neuman-Keuls test to examine differences between the groups. Correlations between 12 preselected variables of interest were analysed by Pearson's correlation coefficient. A two tailed P value of <0.05 was regarded as statistically significant.

The mean (SD) age (years) of women with fibromyalgia syndrome was 46 (12) years, of controls 43 (11) years, and of women with rheumatoid arthritis 51 (13) years, with no significant difference between the patients with fibromyalgia and controls but a significant difference between patients with fibromyalgia and those with rheumatoid arthritis (P<0.01).

Symptoms of restless legs syndrome and leg cramps were significantly more prevalent in patients with fibromyalgia and in those with rheumatoid arthritis than controls (table 1).

Correlation analysis of the patients with fibromyalgia showed no significant correlations between restless legs symptoms or leg cramps and age, pain severity, number of tender points, fatigue, poor sleep, global anxiety, stress, or depression. Paraesthesia, however, correlated with both restless legs (r=0.26, P<0.03) and leg cramps (r=0.17, P<0.05), and muscle cramps correlated with restless legs symptoms (r=0.26, P<0.003).

Comment

Our study shows an association between fibromyalgia syndrome and restless legs syndrome as well as leg cramps and confirms a previously reported association between rheumatoid arthritis and restless legs.3 The basis of this association is not clear. Fibromyalgia is not a psychiatric condition,2 and we found no association between restless legs syndrome and psychological state. It has been suggested that restless legs syndrome and periodic limb movement disorder, along with other dysfunctional syndromes such as irritable bowel syndrome, form a spectrum with overlapping features and a common biophysiological mechanism of neuroendocrine abnormality.2 Such an abnormality may also be the underlying mechanism in restless legs syndrome,5 which is treatable with clonazepam, carbamazepine, and levodopa.1 2 5

In conclusion, restless legs syndrome and leg cramps are significantly more prevalent in patients with fibromyalgia syndrome and those with rheumatoid arthritis than in normal controls. An awareness of this association will help doctors manage the distressing leg symptoms among patients with fibromyalgia.