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SINGLE QUESTION CAN HELP IDENTIFY RESTLESS LEGS SYNDROME
SALT LAKE CITY—The May 2005 FDA approval of ropinirole for treatment of restless legs syndrome sparked increased interest in tools for diagnosing this condition. Wayne A. Hening, MD, PhD, reported at the 20th Anniversary Meeting of the Association of Professional Sleep Societies that a single question makes a reliable screening tool, and a structured telephone diagnostic interview can be used to make a preliminary diagnosis without face-to-face contact.
The question: When you try to relax in the evening or sleep at night, do you ever have unpleasant, restless feelings in your legs that can be relieved by walking or movement?
"This question was designed to be highly sensitive but also to be reasonably specific," said Dr. Hening, who is Assistant Clinical Professor of Neurology at the University of Medicine and Dentistry of New Jersey–Robert Wood Johnson Medical School in New Brunswick.
The question was validated in 85 individuals from a case-control family study of restless legs syndrome—the majority of whom did not have the syndrome—and in 74 individuals with a presumed diagnosis of restless legs syndrome. In the family members, 32 of 33 respondents subsequently diagnosed with restless legs syndrome answered the question positively, as did 10 of 52 in whom restless legs syndrome was subsequently ruled out. That produced sensitivity of 97%, specificity of 81%, positive predictive value of 76%, and negative predictive value of 98%. All 74 of the participants with presumed restless legs syndrome answered positively, for a sensitivity of 100%.
"The single question shows a high degree of sensitivity. This may be especially true for individuals with more severe restless legs syndrome," Dr. Hening said. "Specificity of the single question is lower, but in an acceptable range for a screening instrument: Four fifths of those without restless legs syndrome will answer negatively."
Dr. Hening said that the single question would be useful for making a preliminary selection of subjects with possible restless legs syndrome from an undiagnosed population or to serve as a screening tool for use in clinical practice. "A single valid screening question would provide significant support to the process of reliably identifying those who are likely to suffer from restless legs syndrome. It is important for such a screener to identify all who have restless legs syndrome, but less important (though not unimportant) to exclude those who do not have restless legs syndrome. The assumption is that a definitive diagnosis will require additional questions to ascertain the four diagnostic criteria and to exclude mimics," he said. He warned that because positive predictive value is low, this question will not be an adequate diagnostic instrument for epidemiologic studies. "In a population with 10% true restless legs syndrome, positive predictive value would be only 30%," he said—but those who answer "no" to the question are quite unlikely to have restless legs syndrome and might be used as a control group.
PHONE IT IN
The goal of the telephone interview test was to learn if this instrument, which performed well in tests of restless legs syndrome patients, would function in a nonpatient population, Dr. Hening said. "The telephone diagnostic interview is meant to be an alternative to the gold standard for diagnosis of restless legs syndrome, which requires an expert diagnostic clinical interview." The telephone interview is a set of questions that examine six features of restless legs syndrome:
Leg discomfort
An urge to move
Symptoms that are present at rest
Symptoms that occur frequently when patient is lying down as well as sitting
Symptoms that are relieved by movement
A circadian pattern, with peak symptoms occurring at night or in the evening.
Subjects with all six features were categorized as having definite restless legs syndrome; those with all features except "leg discomfort" and "peak occurrence at night," as having probable restless legs syndrome; and those lacking "urge to move" or lacking "leg discomfort" and "peak occurrence at night," as having possible restless legs syndrome. Diagnoses were confirmed by two blinded clinical interviews.
"Overall agreement was 93%, sensitivity was 92%, specificity was 93%, positive predictive value was 92%, and negative predictive value was 93%," Dr. Hening reported. "This indicates that there will be few false-positives or false-negatives with the telephone diagnostic interview, even when used, as here, on a general population not very familiar with restless legs syndrome."
In four cases the results of the telephone interview and the clinical interview did not agree. Dr. Hening said, "In each case the discrepancy was due to variant information provided by the subjects, rather than to a scoring error by the interviewers."
The telephone interviews had almost as high a rate of agreement with the clinical interviews as the two clinical interviews did with each other, according to Dr. Hening. He noted, however, that these telephone interviews were conducted by an expert in restless legs syndrome and that less experienced interviewers are unlikely to achieve results of this caliber. "We suggest that specific training on the telephone diagnostic interview can increase its usefulness as a confirmatory diagnostic instrument," he said.
NR
—Janis Kelly
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