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

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.

Citation:

Congiu P, Fantini ML, Milioli G, Tacconi P, Figorilli M, Gioi G, Pereira B, Marrosu F, Parrino L, Puligheddu M. F-wave duration as a specific and sensitive tool for the diagnosis of restless legs syndrome/Willis-Ekbom disease. J Clin Sleep Med. 2017;13(3):369–375.

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