Validation of the Multiple Suggested Immobilization Test: A Test for the Assessment of Severity of Restless Legs Syndrome (Willis-Ekbom Disease)

Abstract

Study objectives: To validate the Multiple Suggested Immobilization Test (m-SIT), a symptom-provocation test measuring restless legs syndrome (RLS) severity multiple times a day while the patient is awake and resting under controlled conditions. The m-SIT was designed to overcome some limitations in measuring RLS severity with rating scales.

Design: Patients completed two m-SITs on 2 consecutive days while on 24-h dopaminergic medication. After treatment discontinuation, they completed one more m-SIT 3 days later. Controls performed only one m-SIT.

Setting: Sleep laboratory.

Participants: Nineteen patients with RLS and 10 healthy controls.

Interventions: The original m-SIT consisted of seven modified 60-min SITs performed every 2 h between noon and midnight. During each SIT, the subject reclined quietly but could move his or her legs without restriction to alleviate symptoms. Every 10 min, periodic leg movements during wakefulness (PLMW) were evaluated and the m-SIT Disturbance Scale (m-SIT-DS; range 0-10) was completed.

Measurements and results: The m-SIT, composed of 6:00pm, 8:00pm, 10:00pm, and 12:00pm SITs, discriminated patients from controls (mean m-SIT-DS: 2.68 ± 2.35 versus 0.08 ± 0.26; mean PLMW/h, P = 0.0001) and between treatment groups (on medication versus taken off medication; mean m-SIT-DS, P = 0.0001; mean PLMW/h, P < 0.01). It proved reliable on retest and covariated well with the International Restless Legs Scale (IRLS) and scales measuring daytime symptoms (Spearman ρ > 0.4).

Conclusions: The m-SIT is a valid and reliable test to evaluate RLS severity and treatment response, and could be useful in the future to confirm diagnosis and identify daytime symptoms. Although it was primarily designed for clinical trials, it might be useful in clinical settings because it provides a standardized testing condition to measure RLS symptoms.

Citation: Garcia-Borreguero D; Kohnen R; Boothby L; Tzonova D; Larrosa O; Dunkl E. Validation of the Multiple Suggested Immobilization Test: a test for the assessment of severity of restless legs syndrome (Willis-Ekbom disease). SLEEP 2013;36(7):1101-1109.

Keywords: Daytime symptoms; Willis-Ekbom disease; laboratory tests; restless legs syndrome.

Figures

Figure 1

Mean (A) m-SIT-DS scores and (B) PLMW/h (± standard error) during the m-SIT in patients on medication (m-SIT-1 and m-SIT-2) and taken off medication (m-SIT-3), as well as healthy controls. One control missed a SIT at 10:00pm, so we substituted these m-SIT-DS and PLMW scores with 0. Black bars represent the final 4-SIT combination recommended in this paper. m-SIT-1 versus m-SIT-3: *P < 0.05 and ‡P < 0.0001; controls versus m-SIT-3: †P < 0.05; §P < 0.001. DS, disturbance scale; PLMW, periodic limb movement during wakefulness; m-SIT, Multiple Suggested Immobilization Test.

Figure 2

Frequency distributions of subjects meeting (A and B) mean m-SIT-DS and (C and D) mean PLMW cutoff scores during m-SIT-3 in patients with RLS (A and C) and healthy controls (B and D). Out of the scores shown, cutoff scores of > 2 for mean m-SIT-DS and ≥ 10 for mean PLMW/h were chosen. Black bars represent the final 4-SIT combination recommended in this article. As shown in Figure 2B, none of the controls met these cutoff scores in a single SIT. DS, disturbance scale; PLMW, periodic limb movement during wakefulness; m-SIT, Multiple Suggested Immobilization Test.