Development of a next day functioning measure to assess the impact of sleep disturbance due to restless legs syndrome: the restless legs syndrome-next day impact questionnaire.

OBJECTIVES: Symptoms of Restless Legs Syndrome (RLS) affect patients' quality and duration of sleep, which can have next day sequelae detrimental to daytime performance. To date, no measure sufficiently assesses such sequelae. This study aimed to develop a new self-reported outcome measure to assess the impact of disturbed sleep due to RLS on next day functioning and to support its content validity.
METHODS: The development of the Restless Legs Syndrome-Next Day Impact (RLS-NDI) questionnaire included concept elicitation interviews with RLS patients in the United States (n=20); grounded theory data collection and analysis methods; and review by clinical and measurement experts to generate items, responses, and instructions. Cognitive interviews (n=15) were conducted to ensure understanding of the RLS-NDI, concept comprehensiveness, and identification of any necessary item revisions.
RESULTS: Impacts on next day functioning attributed to disturbed sleep due to RLS symptoms included activities of daily living (i.e., work, household chores), cognitive functioning (i.e., concentration, forgetfulness, mental tiredness, alertness), emotional functioning (i.e., irritability, depressed mood), physical functioning (i.e., physical tiredness, active leisure activities), energy, daytime sleepiness, and social functioning (i.e., relationships, social activities/situations). The final measure consists of 14 items assessed "today" and rated on a numeric rating scale.
CONCLUSIONS: The RLS-NDI is an evaluative tool with demonstrated content validity.