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Original Article

Development of the Pediatric Restless Legs Syndrome Severity Scale (P-RLS-SS)�:A patient-reported outcome measure of pediatric RLS symptoms and impact

Robert Arbuckle a,⇑, Linda Abetz a,1, Jeffrey S. Durmer b, Anna Ivanenko c, Judith A. Owens d,Jens Croenlein e, Kate Bolton a, Adam Moore a, Richard P. Allen f, Arthur S. Walters g,Daniel L. Picchietti h,1

a Mapi Values Ltd., Cheshire, United Kingdomb Georgia State University and Fusion Sleep Medicine Program, Atlanta, GA, USAc Division of Child and Adolescent Psychiatry, Children’s Memorial Hospital, Chicago, IL, USAd Ambulatory Pediatrics, Brown Medical School, Providence, RI, USAe Boehringer Ingelheim Pharma GmbH & Co. KG, Clinical Research CNS, Biberach, Germanyf Department of Neurology, Johns Hopkins University, Baltimore, MD, USAg Department of Neurology, Vanderbilt University School of Medicine, Nashville, TN, USAh University of Illinois School of Medicine, Carle Clinic & Carle Foundation Hospital, Urbana, IL, USA

a r t i c l e i n f o

Article history:Received 20 January 2010Received in revised form 19 March 2010Accepted 25 March 2010

Keywords:Restless legs syndromeSymptomsSleep disorderChildrenPatient-reported outcomeQuality of lifeQuestionnaire developmentAttention-deficit/hyperactivity disorder

a b s t r a c t

Objective: To develop a questionnaire to measure Pediatric Restless Legs Syndrome (P-RLS) symptomsand impact for use in clinical research.Methods: Questionnaire items were developed based on open-ended, qualitative interviews of 33 chil-dren and adolescents diagnosed with definite RLS (ages 6–17 years) and their parents. The draft question-naire was then tested through cognitive debriefing interviews with 21 of the same children/adolescentsand 15 of their parents. This involved the children and parents answering the draft items and then inter-viewing them about the child’s ability to understand and interpret the questionnaire. Expert cliniciansprovided clinical guidance throughout.Results: Draft severity questions were generated to measure the four-symptom and four-impact domainsidentified from the concept elicitation interviews: RLS sensations, move/rub due to RLS, relief from move/rub, pain, and impact of RLS on sleep, awake activities, emotions, and tiredness. RLS descriptions, symp-toms, and impact were compared between those who had comorbid attention-deficit/hyperactivity dis-order and those who did not. Revisions to several questions were made based on the cognitive debriefinginterviews and expert clinician review, resulting in a severity scale with 17 morning and 24 eveningitems. Caution regarding self-administration in children ages 6–8 years is recommended. To complementthe child/adolescent measures, a separate parent questionnaire was also developed.Conclusions: The P-RLS-SS was constructed based on detailed input from children and adolescents withRLS, their parents, and clinical experts, thus providing a scale with strong content validity that is intendedto be comprehensive, clinically relevant, and important to patients. Validation of this scale isrecommended.

� 2010 Elsevier B.V. All rights reserved.

1. Introduction

Pediatric restless legs syndrome (P-RLS) is a relatively commonneurological disorder that can impact sleep, cognition, and affect.First described in detail in 1994, P-RLS is now characterized by asubstantial medical literature that has recently been reviewed

[1–3]. Pediatric-specific diagnostic criteria for RLS were developedat a National Institutes of Health (NIH) workshop and published in2003 [4]. As in adults, the core feature of P-RLS is a prominent urgeto move the legs, usually associated with other uncomfortable andunpleasant sensations. These symptoms typically occur when sit-ting or lying down (e.g., while studying and at bedtime), are re-lieved by movement, and are most severe at night. Early-onsetRLS is highly familial, with recent genome-wide scans having iden-tified five common gene variants associated with RLS [5–10]. Inaddition, periodic limb movements in sleep (PLMS) are presentin the majority of pediatric and adult RLS cases [10–14]. Thepopulation prevalence of P-RLS was recently found to be 2.0% of

1389-9457/$ - see front matter � 2010 Elsevier B.V. All rights reserved.doi:10.1016/j.sleep.2010.03.016

⇑ Corresponding author. Address: Mapi Values, Adelphi Mill, Bollington, Mac-clesfield, Cheshire SK9 5JB, United Kingdom. Tel.: +44 1625 578865; fax: +44 1625577328.

E-mail address: rob.arbuckle@mapivalues.com (R. Arbuckle).1 Senior authors.

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8–17-year-olds in the United States and United Kingdom, withone-quarter of the children and one-half of adolescents reportingmoderate to severe symptoms [15]. This study also described im-pact on cognition and other domains of health-related quality oflife.

Validated severity measures are an essential component of dis-ease assessment for outcomes in clinical trials, particularly for theassessment of symptoms that are known only to the patient, suchas those in P-RLS. In addition, classification of severity can be use-ful for assessment of disease correlates and pathophysiologicalmechanisms as well as clinical treatment decisions. Although bio-metric measures, such as serum glucose in diabetes, are important,patient-reported outcome (PRO) measures are equally important inassessing treatment efficacy. PROs are defined as ‘‘a measurementof any aspect of a patient’s health status that comes directly fromthe patient (i.e., without the interpretation of any aspect of the pa-tient’s responses by a physician or anyone else)” [16] and ‘‘any out-come evaluated directly by the patient himself and based on (the)patient’s perception of a disease and its treatment” [17]. PROs canbe used to measure both single- and multidimensional concepts,such as core symptoms, symptom impact on daily life, ability tofunction, satisfaction with treatment, and physical/psychological/social well-being, the latter often encapsulated by the termhealth-related quality of life (HRQoL). Furthermore, Food and DrugAdministration (FDA) guidelines indicate that fundamental consid-erations in the development or use of a PRO instrument are clearidentifications of the concepts being measured and assurance thatthose concepts are appropriate, well defined, and relevant to thetarget population [16,18,19]. The FDA places particular emphasison demonstrating content validity through performing open-ended interviews with patients who have the disorder beingstudied.

Several PRO scales have been used to assess the severity of RLSin adults. These include the disorder-specific International RestlessLegs Scale (IRLS) [20], Johns Hopkins Restless Legs Severity Scale[21], and Restless Legs Syndrome Quality of Life Questionnaire(RLSQoL) [22], as well as instruments that are generic instruments,such as the Short-Form Health Survey (SF-36) [23,24] and MedicalOutcomes Study Sleep Scale [25]. These have been used to demon-strate that moderate to severe RLS in adults has substantial impacton HRQoL [23,24,26–28].

For P-RLS, a literature search did not identify any severityassessment scales, but one study did look at severity based on pa-tient-reported responses to frequency and intensity questions,which was found to correlate with perceived impact [15]. Thus,there is a need for a validated, disorder-specific P-RLS severityscale. The use of adult measures in children or adolescents is gen-erally inappropriate as wording must be adjusted to age and devel-opmental level, and domains of impact that are relevant to adultsare not always the same ones that are important to children (e.g.,impact on work vs. impact on school) [16]. Child PROs must bedeveloped with consideration of age and developmental limita-tions in children’s vocabulary, memory, attention span, readingability, and the concepts they are able to understand [29,30]. ForHRQoL assessment that is not disorder specific, validated pediatricinstruments are available [31,32].

Of interest, there is significant comorbidity of P-RLS with atten-tion-deficit/hyperactivity disorder (ADHD) in approximately 13–25% of P-RLS cases [10,11,15], and it is estimated that one-quarterof children with ADHD meet diagnostic criteria for RLS [33–35].While the diagnostic criteria for RLS and ADHD are distinct andthere are no shared criteria, four of the DSM-IV criteria for thehyperactive–impulsive subtype of ADHD (items a, b, c, e [36]) re-late to motor activity while seated or to excessive motor move-ment, and could be influenced by the presence of comorbid RLS.In addition, there may be overlap in the respective impact ADHD

and RLS have on cognition, affect, and sleep (e.g., RLS sensationsmight produce inattentiveness, and ADHD-related hyperactivitymight affect sleep onset) [37,38]. Thus, it seems important toinvestigate whether RLS symptom experience or impact is differentfor those who have comorbid ADHD, compared to those who donot.

The specific aim of this study was to develop a multidimen-sional, self-administered, patient-reported outcome questionnaireto assess pediatric RLS symptom severity and impact—the PediatricRLS Severity Scale (P-RLS-SS). Rather than modify an adult RLSseverity scale we sought to develop a new severity measure basedon qualitative interviews with children and adolescents affected byRLS, as well as through input from their parents and guidance by P-RLS clinical experts. Additional objectives were to assess the poten-tial influence of ADHD on P-RLS symptomatology and to assess thefeasibility of a parent version of the P-RLS-SS.

2. Methods

2.1. Severity scale development

The development process followed recommendations from reg-ulatory agencies and PRO experts [16,17,39]. As outlined in Fig. 1,the study involved four main steps: (1) qualitative concept elicita-tion interviews of children/adolescents with RLS and their parents;(2) development of questionnaire items, response options, andinstructions based on the concept elicitation findings, with reviewby an expert panel; (3) cognitive debriefing interviews of the chil-dren/adolescents with RLS and their parents to evaluate face andcontent validity of the draft items; and (4) revisions based on cog-nitive debriefing findings.

2.2. Participants

Participants in both the concept elicitation and cognitivedebriefing interviews were children and adolescents with P-RLS(age range 6–17 years) who were being evaluated at the clinicsof four pediatric sleep disorders specialists in the US (authorsDLP, JSD, AI, JAO). A purposive sampling strategy ensured inclusionof enough participants to achieve ‘‘conceptual saturation” withineach of three age ranges (6–8, 9–11, and 12–17 years). This wasof primary importance, given that children of different ages varyin their ability to self-report using PRO measures [40,41]. Approx-imately equal numbers of children with and without comorbidADHD were included within each age range, to allow comparisonsbetween these groups. The ADHD subgroup had to meet DSM-IVcriteria [36] on clinical assessment and had to have a symptomseverity score 1.5 standard deviations above age and gender normson the ADHD Rating Scale-IV: Home Version, indicating the pres-ence of ongoing ADHD symptoms [42].

In order to participate, the children/adolescents had to fulfillNIH diagnostic criteria for definite RLS (subtype 1 or 2) [4]; haveexperienced RLS symptoms at least once in the two weeks preced-ing the interview; have undergone a physical examination of thelower extremities and demonstrated normal strength, tone, sensa-tion, and reflexes; and be willing to participate. Exclusion wasbased on mental retardation; significant English-language delayor impairment; secondary RLS due to other health conditions suchas renal failure or neuropathy; treatment with stimulant or non-stimulant ADHD medication in the 7 days prior to interview; andtreatment within 14 days prior to interview with medicationknown to significantly influence RLS symptoms (e.g., dopaminer-gics, dopamine blockers, antiemetics, antidepressants, sedatingantihistamines, hypnotics, benzodiazepines, anticonvulsants, clo-nidine, and opioids). Females were excluded if pregnant.

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2.3. Ethics

Copernicus Group Independent Ethical Review Board approvedand oversaw the study, as did local institutional review boardswhere required. Written parental consent and age-appropriatewritten child assent were obtained. Parents were paid $75 andchildren were given a $20 gift voucher following each interview.

2.4. General interview methods

Using semi-structured interview guides, both the concept elici-tation and cognitive debriefing interviews were conducted bytrained, qualitative interviewers, experienced in interviewing chil-dren. For children ages 6–8 years, parents were allowed to be in theinterview room during their child’s interview but were instructednot to influence, answer for, or prompt their child. The remainingchildren and their parents were interviewed separately, unlessotherwise preferred by either the child or parent. All interviewswere audio-recorded and transcribed verbatim.

2.5. Concept elicitation interview

The children were asked to describe the symptoms they experi-enced, what these symptoms felt like, when they were worse orbetter, and what impact the symptoms had on their daily life.The interviews started with very general, open-ended questions(e.g., ‘‘tell me about how your legs feel today”) to avoid leadingthe child. Specific probes were used only if topics of interest didnot arise in response to general questions. Each child’s parentwas interviewed separately about the same issues. The conceptelicitation interviews lasted approximately 1 h and were con-ducted between October 2007 and March 2008.

2.6. Item generation

Based on the qualitative findings of the concept elicitationinterviews, conceptual frameworks for the measurement of P-RLSsymptoms and impact on HRQoL were developed. Instructions,questions, and response options were then generated to measureeach concept. Items and instructions were worded using simple,age-appropriate language and natural phraseology generally usedby children and adolescents (e.g., asking about feeling ‘‘mad”rather than ‘‘frustrated,” and ‘‘sad” not ‘‘depressed”). Items, re-sponse choices, and recall periods were developed to be clearand concise, without using clinical jargon or adult terminology. Apanel of P-RLS and RLS experts provided guidance throughoutthe study, particularly regarding selection and deletion of items(see below). An initial version (v1.0) of the P-RLS-SS, developedbased on the findings of the concept elicitation interviews, waspresented to the Expert Advisory Board in June 2008 to obtainfeedback regarding the clinical appropriateness of the items. Basedon this feedback, instructions, item response options, and concep-tual frameworks were revised.

2.7. Cognitive debriefing interview

Through cognitive debriefing interviews, the children, adoles-cents, and their parents were presented with the revised P-RLS-SS (v2.0) and asked to complete it, speaking their thoughts aloudas they chose a response option for each question. During this pro-cess they were asked further questions about their understandingand interpretation of each question, instruction, and response op-tion, as well as their ability to answer items. They were also askedabout the recall period, its appropriateness, and their ability to re-call over that time period. For some of the children only the morn-ing or evening version was debriefed due to time constraints, and

Fig. 1. Overview of the process for development of the Pediatric Restless Legs Syndrome Severity Scale (P-RLS-SS)�.

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the interview was dependent on the attention span of the child.The cognitive debriefing interviews were conducted in Novemberand December 2008.

2.8. Qualitative analysis

Both concept elicitation and cognitive debriefing interviewtranscripts were coded and analyzed qualitatively using ATLAS.tisoftware (ATLAS.ti GmbH, Berlin, Germany, version 5.2) and usinggrounded-theory methods [43,44]. Experienced qualitative ana-lysts coded the first five interviews. A coding scheme of ‘‘sensitiz-ing concepts” was then developed to guide the remaining analysis[43,44]. The coding scheme could and did change as the data wereanalyzed, but always through discussion among the coders. Exam-ples of codes included ‘‘feels like bugs,” ‘‘things the child does toget relief,” and ‘‘impact of RLS on schoolwork.”

2.9. Expert advisory board oversight

A P-RLS Expert Advisory Board provided clinical/scientific guid-ance throughout the study. The advisory board included four pedi-atric sleep disorder specialists (authors DLP, JSD, AI, JAO) and twoRLS experts who were developers of the adult IRLS Severity Scale(authors RPA, ASW). Key stages where advisory board input wassought included reviewing protocol and study documents, review-ing qualitative analysis results from concept elicitation and cogni-tive debriefing interviews, providing clinical input into developingand revising each version of the P-RLS-SS, and writing/reviewingthe manuscript.

3. Results

3.1. Demographics and clinical characteristics

3.1.1. Concept elicitationThirty-three children and adolescents with definite RLS, ages 6–

17 years, participated in the concept elicitation interviews. Table 1provides a summary of age and gender stratification according todiagnosis of definite RLS with or without ADHD. All 33 met criteriafor ‘‘definite 1” RLS [4]. For ‘‘definite 1” RLS the child must be able todescribe leg sensations in their own words and meet all 4 adult cri-teria for RLS: (a) an urge to move the legs; (b) symptoms worse atrest, i.e., lying or sitting; (c) at least partial and temporary relief ofsymptoms while actually moving; and (d) symptoms worse later inthe day or at night. Fourteen (42%) were female and 15 (45%) hadbeen diagnosed with ADHD. Mean age was 11.2 years (SD ± 3.3;range 6.2–17.5). All 33 were diagnosed by one of four pediatricsleep disorders specialists (authors DLP, JSD, AI, JAO) and theseclinicians differentiated RLS from mimics such as positional dis-

comfort, sore muscles, ‘‘growing pains,” leg cramps, and joint com-plaints. The majority was Caucasian (91%) and three were AfricanAmerican (9%). The most common other medical problems re-ported were allergies (42%), asthma (27%), and anxiety problems(18%). One of each child/adolescent’s parents was also interviewed.These 33 cases are included in a related publication, which empha-sizes descriptions and drawings of pediatric RLS rather than thedevelopment of a severity scale [45].

3.1.2. Cognitive debriefingTable 1 also provides a summary of age and gender stratifica-

tion according to diagnosis of RLS for the cognitive debriefing sam-ple. Twenty-one of the children/adolescents who participated inthe concept elicitation returned to participate in the cognitivedebriefing interviews. This sample was considered adequate togain an understanding of the ability of children of different agesto complete the questionnaire; therefore the remaining partici-pants were not asked to participate in the cognitive debriefing por-tion of the study. Ten (48%) were female and 10 (48%) hadcomorbid ADHD. Mean age was 10.6 years (SD ± 3.3; range 6.2–16.6). The majority was Caucasian (86%) and three were AfricanAmerican (14%). The most common other medical problems wereallergies (33%), asthma (19%), and anxiety problems (19%). Inter-views with parents of 15 of these children were also conducted.

In both the concept elicitation and cognitive debriefing samplesthere were no significant age, gender, or race differences betweenthe participants with and without ADHD.

3.2. Concept elicitation results

3.2.1. Conceptual frameworkThematic analysis of the concept elicitation interviews identi-

fied four-symptom and four-impact/HRQoL domains. A conceptualframework was developed based on these findings and is providedin Fig. 2. The findings for these domains and the items developed tomeasure each domain are summarized below, and example quotesare presented in Appendix A, Table 1, Supplementary Material. Amore detailed symptom and impact description analysis will bepublished separately [45].

3.2.2. Recall periodFindings suggested that children of all ages had little difficulty

recalling symptoms over 24 h, but, if asked to recall over a longertime period, younger children in particular would have difficultyrecalling accurately.

3.2.3. Timing of RLS symptomsAll children/adolescents reported experiencing symptoms at

night, most commonly when trying to fall asleep. In addition, day-time leg sensations were described by 22 of the children/adoles-

Table 1Concept elicitation and cognitive debriefing samples by age, gender, and ADHD subgroups.

Diagnoses Age 6–8 years Age 9–11 years Age 12–17 years Total

Male Female Male Female Male Female

Concept elicitationDefinite RLS without ADHD 5 1 3 3 3 3 18Definite RLS + ADHD 2 2 3 2 3 3 15

Total 10 11 12 33

Cognitive debriefingDefinite RLS without ADHD 2 3 1 2 2 1 11Definite RLS + ADHD 2 2 1 1 3 1 10

Total 9 5 7 21

RLS, restless legs syndrome; ADHD, attention-deficit/hyperactivity disorder.

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cents (67%). Thus, the P-RLS-SS was developed to be answeredtwice daily, first thing in the morning with a recall period of‘‘when you were in bed last night” and in the evening with a recallperiod of ‘‘today.” All symptom questions are included in bothmorning and evening diaries. Some impact questions are onlyappropriate to be asked at one time or the other; for example,questions about difficulty falling asleep are only appropriate inthe morning diary.

3.3. Item generation

3.3.1. RLS sensationsEvery child/adolescent reported experiencing uncomfortable

feelings in their legs, overall using many different terms to describethese sensations. These included ‘‘crawling/like bugs or ants,”‘‘weird/funny feelings,” ‘‘tingling,” like ‘‘nails/pins/needles” pokingtheir legs, ‘‘wiggling,” ‘‘pulling,” and ‘‘fizzing/popping” sensations

Fig. 2. Conceptual framework of the Pediatric Restless Legs Syndrome Severity Scale (P-RLS-SS)�.

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in their legs. One child spoke of ‘‘tired” legs and a number of par-ents also reported this of their children. To capture the wide rangeof descriptions, the opening item in the draft P-RLS-SS (v1.0) asked,‘‘Did your legs: feel creepy–crawly; feel like ants were crawling onthem; feel like something was poking them; feel like somethingwas pulling inside them; feel wiggly; feel like something was pop-ping inside them; feel tired; feel tingly; feel weird; feel like some-thing was fizzing inside them.” The potential responses for eachdescriptor were ‘‘yes,” ‘‘no,” or ‘‘I don’t know.”

Children/adolescents mentioned experiencing the leg sensa-tions lying in bed, sitting in school, in church, in a car, at meal-times, when sitting watching television/movies, and whenreading. Based on these comments, an item was developed askingwhether the RLS feelings were experienced while lying, sitting,standing, and/or walking around.

Sixteen children/adolescents (48%) reported experiencing RLSsensations in their arms and/or hands. Thus, items were developedasking whether the children got ‘‘these feelings” in their arms, andhow bad the feelings in their arms were. However, it should benoted who almost all that experienced arm/hand sensations indi-cated that these were far less frequent and severe than those intheir legs.

3.3.2. Movement/rubbing due to RLSThe majority of the children/adolescents (n = 23; 70%) described

a need to move their legs when describing their RLS symptoms. Asthe children (and their parents) reported a range of ways the feel-ings might make them move their legs, four items were includedasking if the RLS feelings made the child wiggle, stretch, kick, orrub their legs that day or night. An item was also developed askingif RLS sensations made the child ‘‘get up and walk around.” Sug-gested by P-RLS experts in response to some of the descriptions,two items were also included asking whether the RLS sensationsmade the children ‘‘hit” their legs.

3.3.3. Relief from moving/rubbing legsIn addition to moving or rubbing their legs, almost all children/

adolescents spoke of getting some degree of relief from the RLSfeelings with these actions. Thus, for each of the ‘‘movement/rub-bing” items, a corresponding item was included asking whetheror not the movement/action resulted in relief (e.g., ‘‘Did kickingyour legs make the feelings go away? Yes, they went away com-pletely; yes, they went away a little but came back; or no; I don’tknow”).

3.3.4. RLS hurting/painfulMany children/adolescents of all ages (n = 15; 45%) described

their RLS feelings as ‘‘hurting” or being ‘‘painful” during the con-cept elicitation interviews. They suggested that the RLS sensationsbecame painful if they ignored them or if they were having a par-ticularly severe episode. An example quote is as follows: Q: ‘‘Doesit ever hurt when you get that ‘‘have to kick feeling” in your leg?”A: ‘‘If I don’t do it, then it really hurts” (9 y, female). Therefore, be-cause pain could be a good indicator of severity, an item was in-cluded that asked, ‘‘Did these feelings in your legs hurt today/lastnight?”

3.3.5. RLS impact on sleepSleep problems were reported by almost all children/adoles-

cents across all age groups (n = 29; 88%). Specifically, they talkedabout difficulties falling asleep (n = 26; 79%) and waking duringthe night (n = 13; 39%) due to RLS sensations. Questions were in-cluded in the morning diary asking, ‘‘Did the feelings in your legsmake it hard to fall asleep last night?” as well as ‘‘How many timesdid you wake up last night?” Based on expert feedback, an itemasking, ‘‘Did these feelings in your legs wake you up last night?”

was also included. It was recognized that it might be difficult forthe children to attribute waking as being due to RLS, but it was feltto be worth testing through cognitive debriefing.

3.3.6. RLS impact on wake activitiesA number of the children/adolescents made comments regard-

ing the impact of RLS during the day. This included disruption ofactivities that required them to sit still and to concentrate. Thus,six items were included in the P-RLS-SS to assess whether theRLS feelings made it hard to sit at their school desk, do school work,do homework, read, watch TV, or play video games. All six itemshad the three response options: ‘‘yes, very hard; yes, a little; no.”

3.3.7. RLS impact on emotionsThe children/adolescents reported various ways that RLS

affected their emotional well-being, including making them feelsad, angry, and annoyed. Thus, two items were developed askingthem if the feelings in their legs made them ‘‘feel sad” or ‘‘mador angry.” While only one child reported feeling ‘‘grumpy” becauseof RLS, a number of parents described their child as being irritable,so it was considered appropriate to develop an item asking aboutfeeling ‘‘grumpy or cranky,” child-friendly words recommendedby the pediatric clinicians. The P-RLS experts also suggestedincluding an item asking about general emotional well-being,worded, ‘‘How do you feel this morning/evening?” with a faces re-sponse scale similar to the Wong-Baker Faces Scale [46,47].

3.3.8. RLS impact on tirednessTwenty-three children/adolescents (70%) talked about feeling

tired or sleepy during the day, most attributing this to sleep distur-bance from RLS sensations the previous night or as a consequenceof having to deal with constant RLS sensations. Based on these re-ports, an item asking, ‘‘How tired are you today?” was included inthe evening questionnaire. Similarly, an item was included in themorning questionnaire asking how tired the child felt thatmorning.

3.3.9. Conceptual saturation and differences by age, gender, and ADHDConceptual saturation is defined as the point at which no new

concept-relevant information emerges from further interviews[39,44]. Saturation of all concepts included in the P-RLS-SS wasachieved in all age groups, and in those with and without ADHD.There were no substantial differences in the concepts reported bydifferent age groups. As might be expected, there was some evi-dence of older children/adolescents using more sophisticated lan-guage than younger children—but even some younger childrengave quite elaborate and detailed descriptions of the RLS sensa-tions. Younger children more often used the words ‘‘kick” and‘‘wiggly” to describe their RLS sensations. In contrast ‘‘tingling”was only used by those ages 11 or older. No consistent gender dif-ferences were evident except that younger boys seemed to havemore difficulty giving details about the RLS feelings compared toyounger girls. There were no substantial differences in descriptionsof concepts, RLS symptoms, or impact between those who hadcomorbid ADHD and those who did not. Surprisingly, difficultyconcentrating, difficulty sitting, and irritability due to RLS sensa-tions were reported equally often.

3.3.10. Response optionsEach of the items was developed with as few response options

as possible, due to concerns that children may not be able to differ-entiate between more than four or five Likert-type response op-tions. Where appropriate, faces similar to the Wong-Baker painfaces were added to the response options to make them moreengaging and easy to understand [46,47].

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3.3.11. Expert Advisory Board reviewFeedback from the advisory board informed revisions to the

draft questionnaire (v1.0) prior to the cognitive debriefing inter-views. Care was taken to ensure that the items still reflected thequalitative findings of the interviews.

3.3.12. Summary of item generationIn the resulting P-RLS-SS, v2.0, there were 26 morning and 28

evening items. These included presence and severity of RLS sensa-tions (four morning and five evening items); moving/rubbing legsdue to RLS (seven items, both morning and evening); relief ofRLS sensations with moving/rubbing (seven items, both morningand evening); painful sensations (one morning and one eveningitem); and impact of RLS symptoms on sleep (three items, morn-ing), awake activities (six items, evening), emotions (three morn-ing and one evening items) and tiredness (one morning and oneevening item).

3.4. Cognitive debriefing of the P-RLS-SS

Almost all children, adolescents, and parents found the majorityof the P-RLS-SS (v2.0) items, instructions, and response optionsstraightforward and easy to understand. The majority of the chil-dren and adolescents reported that items accurately captured thefeelings they experienced in their legs and throughout the cogni-tive debriefing, and most were able to correctly interpret themeaning of items and put them in their own words. Many childrenalso commented on their willingness to complete the P-RLS-SS fora 2-week period as part of a study.

Despite generally positive feedback, 10/21 children and adoles-cents had difficulty answering one or more items, while others feltthat several items were redundant. However, only two children(ages 6 and 7 years) had comprehension difficulties with morethan one item. Of note, those children who had difficulty were pre-dominantly ages 6–8 years, suggesting that children this youngmay not have the cognitive and/or reading abilities to completethe questionnaire alone. In addition to the comprehension prob-lems, 5/24 children (ages 9–14 years) stated they had difficultyanswering a question due to being unable to recall over the speci-fied recall period. This was particularly a problem for the questionsasking about waking during the night. Further details of the com-prehension and recall difficulties are summarized in Appendix A,Supplementary Material.

3.5. Revision of the P-RLS-SS

Based on the child, adolescent, and parent cognitive debriefingresults, a number of changes were made to the P-RLS-SS, includingdeletion of several items. Also, there was additional review by theExpert Advisory Board. Details of the changes are provided inAppendix A, Tables 2 and 3, Supplementary Material. These includeaddition of ‘‘. . .did your legs: Feel like they needed to move?” and‘‘. . .did your legs: Feel like they needed to kick?” to the first ques-tion of the morning and evening scales, to capture the ‘‘urge tomove” component. The six descriptors for P-RLS in the scale (Ques-tion 1) were chosen to represent the core RLS sensory experiencebased on frequency of use by children/adolescents, specificity forRLS, cognitive debriefing, and expert feedback. Pain was not chosenas a primary descriptor because pain is commonly used to describethe potential mimics of RLS. The resulting P-RLS-SS (v3.0; Appen-dix B, Supplementary Material) has 17 morning and 24 eveningitems, which follow the conceptual framework in Fig. 2. Two rep-resentative items are presented in Fig. 3.

3.6. P-RLS-SS parent questionnaire (P-RLS-SS-PQ�)

During the Expert Advisory Board meeting, it was recom-mended that a parent questionnaire should be developed to com-plement the child/adolescent measures. Parents more oftennoticed behaviors such as unusual sleeping patterns and irritabil-ity, and therefore a set of parental items was generated. These in-clude parental ratings of RLS symptom severity (how much a childcomplained about sensations/how much a child kicked their legs)and impact (sleep problems, tiredness, and difficulties sitting stillor doing schoolwork/homework). The P-RLS-SS-PQ also includesitems assessing impact on the parent (sleep disturbance, frustra-tion, and worry due to their child’s RLS). Although developed atthe suggestion of the advisory board, the P-RLS-SS-PQ is basedon qualitative data from the parent concept elicitation interviewsand focuses on observable behaviors or verbal complaints fromchildren to their parents. The resulting P-RLS-SS-PQ has 20 items(Appendix C, Supplementary Material). This scale is intended tosupplement information from the child/adolescent scale, not tobe an independent measure of P-RLS.

4. Discussion

Development of the P-RLS-SS addresses the need for a disorder-specific, age-appropriate PRO measure of RLS symptoms andimpact that is appropriate for use in children and adolescents.Rigorous methodology was followed and the resultant 41-itemscale incorporates numerous pediatric features, such as simplifiedlanguage and a 24-h recall period. As with other conditions, likemigraine headache, where there are significant sensory symptoms,accurate, valid measurement of self-reported symptoms andimpact is very important for clinical research.

There is evidence in the literature that children as young as6 years can use a rating scale to report somatic sensations[30,48]. In the present study, the following steps were taken to in-crease the likelihood that the questionnaire would be understoodby children as young as six: questions were worded to be as shortand simple as possible; a maximum of five response options were

Fig. 3. Two representative items from the Pediatric Restless Legs SyndromeSeverity Scale (P-RLS-SS)�: a symptom item from the evening questionnaire andan impact item from the morning questionnaire.

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used for each item; and faces adapted from the Wong-Baker Painfaces scale were used in the response options, where appropriate[46,47]. Based on cognitive debriefing, further refinements weremade to the P-RLS-SS to make it even easier for children to com-plete. Confusing or redundant items were deleted or modifiedand response options were added to many of the items in responseto requests from a number of children of all ages.

Evidence from both the concept elicitation and cognitivedebriefing interviews suggests children ages nine and older willbe able to reliably report their RLS symptoms using the P-RLS-SS.The evidence regarding children ages 6–8 years is more equivocal,suggesting that some children ages 6–8 may not have the readingor cognitive abilities to answer some questions, as has been foundin other samples [29]. Nevertheless, other children of this age wereable to complete the questions with very little difficulty. Thus, it isbelieved that the questionnaire can be used with confidence inchildren ages P9 and with caution in children ages 6–8. Revisionsmade following cognitive debriefing should address the non-age-related difficulties identified.

The concept elicitation interviews with children, adolescents,and their parents ensured that the draft P-RLS-SS was comprehen-sive, covering all symptoms that were important to patients. Clini-cians reviewed the P-RLS-SS for clinical relevance, while children,adolescents, and parents reviewed the P-RLS-SS for relevance andease of understanding. These methods and the subsequent resultsensure strong face and content validity [39,49].

The adult IRLS rating scale has been used extensively in clinicaltrials as a measure of the severity of adult RLS [20,50–52]. Compar-ing the final P-RLS-SS and the adult IRLS, they are consistent in theconcepts they measure—both ask about symptom severity, theurge/need to move, relief from movement, and impact on sleep,daily activities, mood, and tiredness. The two measures differ con-siderably in the number and wording of items and response op-tions used. The P-RLS-SS uses more child-appropriate wording,has more items, and has a shorter recall period, reflecting the cog-nitive capabilities of children [29]. For example, using words suchas ‘‘urge,” ‘‘discomfort,” and ‘‘severe” would be inappropriate for achild measure. In addition, the P-RLS-SS asks about specific dailyactivities relevant to children but not adults, such as doing school-work. Thus, the two measures can be considered conceptuallyequivalent, while each has age-appropriate content.

The items of the P-RLS-SS were developed with the intentionthat they would be administered as an electronic PRO (e-PRO) ona personal data assistant (PDA). An ePRO would allow skip patternsto be used, thus minimizing participant burden—particularlyimportant in a pediatric population and for a diary with as manyitems as the P-RLS-SS. However, due to funding limitations it wasonly possible to cognitively debrief a paper version. Thus, eithera paper or a PDA version could be used in future studies, but cog-nitive debriefing of a PDA version is recommended before it is usedin a larger study.

Prior to use in clinical research, psychometric validation of theP-RLS-SS in a larger sample is important to provide evidenceregarding its validity and reliability, as well as address issues suchas severity score relevance. Data yielded might also inform furtheritem reduction if psychometrics demonstrate that a shorter versionwould be adequate to assess P-RLS symptom severity. However,item deletion should not be based on psychometric validation re-sults alone—the concept elicitation results and clinical relevanceof items should also be considered.

We were somewhat surprised that there were not qualitativedifferences in P-RLS concepts, symptoms, or impact as describedby children with RLS and comorbid ADHD, compared to those withRLS alone. However, based on some [53–56] but not all [34] previ-ous research we hypothesize that there may be quantitative differ-ences, particularly in the severity of symptom impact. For example,

the presence of RLS feelings during the day or of RLS-related sleepdisturbance at night could increase inattentiveness at school. Con-versely, difficulty ignoring extraneous stimuli (the RLS sensations)in ADHD may increase the impact of RLS on cognitive tasks. The P-RLS-SS, along with available ADHD severity scales, should be help-ful in measuring this potential bidirectional impact.

An additional concern related to RLS/ADHD comorbidity is thepotential influence on diagnosis. Because leg sensations (urge ordiscomfort) are not part of the ADHD diagnostic criteria, ADHD isunlikely to be misdiagnosed as RLS. However, since symptoms ofRLS could both directly mimic ADHD symptoms (i.e., hyperactivity)and indirectly result in daytime symptoms that overlap with thoseof ADHD (i.e., inattentiveness), this could result in a misdiagnosisof ADHD. Nonetheless, it may be very difficult to ascertain the cau-sality of inattention or hyperactivity in individual cases. Further-more, there may be an underlying dopaminergic and/or irondeficit driving both RLS and ADHD symptomatology in some cases[38]. Consequently, we think that assessment by standard diagnos-tic criteria for both disorders is important in clinical and researchsettings, with additional focus on how the conditions mightinteract.

4.1. Limitations

In addition to the comments above on age, method of adminis-tration, and further validation, other limitations of this studyshould be considered. We did not include children less than 6 yearsof age because they are not likely to be able to self-report P-RLSsymptoms and their impact in a reliable way due to limited lan-guage skills and cognitive immaturity. Because PLMS play a largerrole in assessment of these young children [4,57], work on legmovement monitors for repeat measurement of PLMS as a markerof severity is warranted. Also, parent-reported measures could beparticularly helpful, suggesting further refinement of the P-RLS-SS-PQ, which was developed as part of this project. Finally, thisstudy sampled a US, clinical population that was predominantlyCaucasian, limiting applicability to other populations.

5. Conclusions

The P-RLS-SS is a self-administered, disorder-specific ratingscale that has strong content validity and is appropriate to measuresymptoms in children as young as 9 years old. Valid measurementof P-RLS severity will help further research in this common disor-der, including the assessment of treatment efficacy, identificationof children for whom treatment is appropriate, and explorationof the relationship of severity to comorbidity.

Disclosure statement

Drs. Picchietti, Durmer, Ivanenko, and Owens have served asconsultants to and have received research support from BoehringerIngelheim for this project; Dr. Picchietti has been a consultant forGlaxoSmithKline; Mr. Arbuckle and Mrs. Abetz are employees ofMapi Values Ltd., a health outcomes research agency, and werecontracted by Boehringer Ingelheim to work on this project; Dr.Croenlein is an employee of Boehringer Ingelheim Pharma GmbH& Co. KG; Dr. Allen has received research support from and hasserved as a consultant for Boehringer Ingelheim and GlaxoSmithK-line; and Dr. Walters has received research support from, has actedas a consultant for, and has served on a speakers bureau for Boeh-ringer Ingelheim and GlaxoSmithKline.

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Acknowledgements

The authors thank the children and adolescents with RLS andtheir parents who participated in the interviews. For their assis-tance in organizing and sponsoring this project, we acknowledgeDr. James Cappola and Boehringer Ingelheim. We would also liketo thank Kathy Lasch, Cathy Podeszwa, Sara Strzok, and KristinaFitzgerald for conducting the interviews. Author sequence wasdetermined using ‘‘first, second, and last author emphasis” format,based on scientific contributions.

The P-RLS-SS� questionnaire is protected by copyright, regis-tration at US copyright office, #PRE000002941. Do not use orreproduce without permission. For any information or permissionto use the questionnaire, please contact: MAPI Research Trust,Lyon, France. E-mail: contact@mapi-trust.org; Internet: www.mapi-trust.org.

This project was supported by Boehringer Ingelheim Pharma. P-RLS-SS� Boehringer Ingelheim Pharma, 2010, all rights reserved.

Appendices A–C. Supplementary material

Supplementary data associated with this article can be found, inthe online version, at doi:10.1016/j.sleep.2010.03.016.

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