Objective: To assess the frequency of restless legs syndrome (RLS) in patients with functional movement disorders (FMD).

Background: Sensations related to RLS are varied, often reported as unusual and they could mimic functional sensory symptoms in FMD. RLS diagnosis is clinical and can be supported using actigraphic assessment of periodic limb movements (PLM).

Methods: Ninety five consecutive patients with clinically established FMD (77 females, mean age 44.4±13(SD), mean disease duration 6.1±5 years) and 57 matched healthy controls were interviewed by movement disorders expert for the presence of RLS according to the criteria of the International RLS Study Group. Information on presence of sensory symptoms, organic comorbidities and use of antidepressants was obtained. All subjects completed questionnaires for evaluation of chronic pain, depression, anxiety trait, fatigue and daytime sleepiness. For detection of PLMs, actigraphy from big toes over three nights was recorded. The PLM index (PLMi) was calculated and value ≥ 22.5 in at least one night was used as cut-off for clinically relevant PLM. We analyzed the differences in these variables between RLS positive (RLS+) and negative (RLS-) patients and controls.

Results: FMD patients had higher scores of organic comorbidity, antidepressant use, chronic pain, depression, anxiety trait, fatigue and daytime sleepiness than controls (p<0.001). Sensory symptoms were present in 75 FMD patients (81.5%) and only in 4 controls (7%). After exclusion of all mimics including symptoms suggestive of functional etiology, RLS was diagnosed conservatively in 43 patients (45.3%, 95% CI 35.6 – 55.3) and in 5 controls (8.9%, CI 3.9 -19.3%; p<0.001); 22.1% (CI 14-33%) of patients were RLS+ and had PLMi≥22.5. FMD patients had higher mean PLMi than controls (21.6±19 vs 10.1±15; p<0.001). RLS+ patients had higher mean PLMi than RLS- (29±21 vs 15.1±13, p<0.01), higher proportion of PLM ≥ 22.5 (42.8 vs 10%; p<0.001) and more severe fatigue (p<0.5) but no difference in age, use of antidepressants and organic comorbidity or other variables was found.

Conclusions: We found a high prevalence of RLS in our group of FMD patients. The presence of RLS was associated with higher proportion of clinically relevant PLM and more severe fatigue.  RLS may be under-recognized in FMD and a detailed clinical evaluation may help to differentiate RLS from functional sensory symptoms and to start effective treatment of RLS.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/restless-legs-syndrome-in-functional-movement-disorders/