Neuropathy in a cohort of restless leg syndrome patients

Abstract

This study aims to evaluate the types of neuropathy in a cohort of restless leg syndrome (RLS) patients and compare them with primary RLS. RLS symptoms can occur in peripheral neuropathy and may cause diagnostic confusion, and there is a paucity of studies comparing neuropathic RLS and primary RLS. Patients with RLS diagnosed according to the international restless legs syndrome study group criteria were categorized as primary RLS or secondary. Those with evidence of peripheral neuropathy were categorized as neuropathic RLS. The demographic, clinical, laboratory profile and therapeutic response to dopamine agonists at 6 months and 1 year of neuropathic RLS patients were compared between primary and secondary RLS patients. There were 82 patients with RLS of whom 22 had peripheral neuropathy and 28 had primary RLS. The etiology of neuropathic RLS was diabetes mellitus in 13, renal failure in six, hypothyroidism in five, demyelinating in two, nutritional deficiency in three, leprosy in one, and miscellaneous etiologies in four patients. The neuropathic RLS patients were older (46.0 ± 14.1 versus 35.8 ± 15.4 years), had shorter duration of illness (1.4 ± 1.4 versus 6.2 ± 6.2 years) and were more frequently symptomatic. RLS symptoms were asymmetric in primary RLS patients compared to neuropathic RLS (25% versus 0%). The therapeutic response was similar in both groups.

Introduction

Restless leg syndrome (RLS) is a sensorimotor sleep-related movement disorder manifesting with an urge to move the legs and unpleasant sensation in the lower limbs. The prevalence of RLS in the general population is 5 to 15% [1], [2]. RLS may be primary or secondary, the latter is associated with a number of disorders like diabetes mellitus, renal failure, iron deficiency and peripheral neuropathy, rendering the diagnosis difficult [3]. There is marked variation in the prevalence of RLS in neuropathies and the reported prevalence ranges from 5.2 to 54% [4], [5]. The symptoms of RLS are often difficult to characterize and patients often find it difficult to describe their symptoms. A large number of terms are used to describe RLS symptoms such as tingling, pain and paresthesia, current-like or shock-like sensations, and in one study, 7% of patients found it difficult to distinguish dysesthesia from pain [6]. Typically, RLS symptoms have a circadian pattern and are worse in the evening or at night. The symptoms in neuropathy, especially axonal neuropathy and small fiber neuropathy, can also have similar or overlapping symptoms. Additionally, in some neuropathy patients, neuropathic symptoms are also worse at night. RLS has been reported with a number of neuropathies such as diabetes mellitus, renal failure, Charcot–Marie–Tooth disease, cryoglobulinemia and various painful neuropathies [4], [5], [7], [8], [9], [10], [11]. RLS is thought to be more common in small fiber, painful neuropathies compared to large fiber neuropathies (54% versus 5.2%, respectively) [4], [5]. However, a blinded randomized study did not find any difference in the prevalence of RLS in neuropathy compared to controls [12]. The difference in the prevalence of RLS in neuropathies has been attributed to different study design, different nature and etiology of polyneuropathy and the extent of evaluation for neuropathy and RLS. There are very few studies on the association of neuropathy with RLS in developing countries where the spectrum of neuropathy may be different and RLS may be poorly recognized. Therefore, we have undertaken this study to assess the incidence of neuropathy in patients with RLS and to characterize the difference between RLS patients with neuropathy and those with primary RLS.