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. 2017 Mar 15;13(3):369-375.
doi: 10.5664/jcsm.6482.

F-Wave Duration as a Specific and Sensitive Tool for the Diagnosis of Restless Legs Syndrome/Willis-Ekbom Disease

Patrizia Congiu  1 , Maria Livia Fantini  2 , Giulia Milioli  3 , Paolo Tacconi  4 , Michela Figorilli  1 , Gioia Gioi  1 , Bruno Pereira  5 , Francesco Marrosu  4 , Liborio Parrino  3 , Monica Puligheddu  1
Affiliations

F-Wave Duration as a Specific and Sensitive Tool for the Diagnosis of Restless Legs Syndrome/Willis-Ekbom Disease

Patrizia Congiu et al. J Clin Sleep Med. .

Abstract

Study objectives: Restless legs syndrome, also known as Willis-Ekbom disease (RLS/WED), is a frequent condition, though its pathophysiology is not completely understood. The diagnosis of RLS/WED relies on clinical criteria, and the only instrumental tool, the suggested immobilization test, may lead to equivocal results. Recently, neurophysiological parameters related to F-wave duration have been proposed as a diagnostic aid. The aim of this study is to assess and compare the diagnostic values of these parameters in diagnosis of RLS/WED.

Methods: Fifteen women affected by primary RLS/WED and 17 age- and sex- matched healthy subjects. A complete electroneurographic evaluation, including nerve conduction studies (NCS), cutaneous silent period (CSP), and F-wave parameters, namely amplitude, F-wave duration (FWD), and the ratio between FWD and duration of the corresponding compound muscle action potential (FWD/CMAPD).

Results: No subject showed alterations of the NCS. However, FWD and FWD/CMAPD of both upper and lower limbs were significantly longer in patients than controls. Tibial FWD/CMAPD best discriminated RLS/WED patients from controls. A cutoff of 2.06 yielded a sensitivity of 69.2%, a specificity of 94.1%, a positive predictive power of 90%, and a negative predictive power of 80% (area under the curve = 0.817; 95% confidence interval = 0.674-0.959). The combination of ulnar or tibial FWD/CMAPD increases the sensitivity (85.7%) while slightly decreasing the specificity (87.5%, positive predictive value: 85.7%, negative predictive value: 87.5%).

Conclusions: Lower limb FWD/CMAPD ratio may represent a supportive diagnostic tool, especially in cases of evening lower leg discomfort of unclear interpretation.

Keywords: F waves; diagnostic tool; restless legs syndrome/Willis-Ekbom disease.

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Figures

Figure 1
Figure 1. F waves of tibial nerve in a patient with restless legs syndrome (RLS) and in a control subject.
CMAP = compound muscle action potential, CMAPD = compound muscle action potential duration, FWD = F-wave duration.
Figure 2
Figure 2. Cutaneous silent period (CSP) of the anterior tibialis muscle (AT) in a patient with restless legs syndrome (RLS) and in a control subject.
Figure 3
Figure 3. Receiver operating characteristic curves for tibial and ulnar nerve F-wave duration parameters.
Continuous black line = tibial FWD/CMAPD, dotted black line = tibial FWD, continuous gray line = ulnar FWD/CMAPD, dotted gray line = ulnar FWD. CMAPD = compound muscle action potential duration, FWD = F-wave duration.
See this image and copyright information in PMC

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