Quantitative transcranial sonography of the substantia nigra as a predictor of therapeutic response to intravenous iron therapy in restless legs syndrome.

OBJECTIVE: To analyze changes in substantia nigra (SN) iron deposits, assessed by quantitative transcranial sonography (TCS), to obtain and compare substantia nigra echogenicity indices (SNEI) at baseline and after intravenous (IV) iron therapy in patients with restless legs syndrome (RLS)/Willis-Ekbom disease (WED). METHODS: A total of 30 consecutive subjects diagnosed with RLS/WED were recruited and underwent IV iron treatment. The SNEI, total daily dose of dopamine equivalents, and International Restless Legs Syndrome Rating Scale (IRLS) scores were obtained at baseline and following IV iron administration. Comparative statistics were performed by means of nonparametric testing. RESULTS: The sample was stratified into two groups according to the median baseline SNEI and the grade of SN hypoechogenicity: severely hypoechogenic (HE) (n = 13) and moderately HE (n = 17). Following IV iron, the increase in SNEI among severely HE subjects was 19% (0.038 ± 0.046 cm2; P < 0.01), whereas in moderately HE subjects it was 10% (0.021 ± 0.069 cm2; P = 0.28). Among severely HE subjects, the average reduction in IRLS following IV iron was 10 ± 7.12 points (P < 0.01), in contrast to 1.85 ± 9.85 (not significant) among moderately HE subjects. Finally, we quantified the percentage of patients in each group who were able to reduce by ≥30% their total daily dopaminergic requirements (TDR) after IV iron, with a 57.14% reduction in the severely HE group vs 25% in the moderately HE group (P = 0.1). Three of 30 subjects (17%) were able to completely cease all dopaminergic treatment. CONCLUSION: Intravenous iron caused changes in SNEI in both groups of patients, reflecting an increase in brain iron stores. However, the increase in SNEI was greater in patients previously defined as severely HE. Furthermore, RLS/WED symptoms also improved more in severely HE subjects, and there was a greater reduction in TDR. This study highlights the role of TCS in quantifying brain iron deposits and in predicting which patients will likely benefit from IV iron.

Non-dopaminergic vs. dopaminergic treatment options in restless legs syndrome.

Two types of drugs have been extensively investigated for the treatment of restless legs syndrome (RLS)/Willis-Ekbom disease (WED): dopamine agonists and α2δ ligands to the α2δ subunit of calcium channels. Comparative studies show that both classes of drugs are similarly effective in treating RLS symptoms over the short- and long-term. While dopamine agonists are more effective in treating periodic limb movements (PLMs), α2δ ligands are more effective in consolidating sleep. However, given the fact that dopamine agonists cause high rates of augmentation of symptoms, recent international guidelines recommend that whenever possible the initial treatment of choice should be an α2δ ligand. In fact, the most effective preventive strategy involves not using dopaminergic agents unless absolutely necessary. Indeed, should dopaminergic treatment be needed to handle the symptoms effectively, then it is recommended that the dopaminergic load be reduced by using the lowest effective dose for the shortest possible period of time. However, it must be taken into account that the only α2δ ligand approved for RLS/WED is gabapentin enacarbil, which is not yet available in Europe. Furthermore, recent studies have also reported on the efficacy of opioids as a second-line treatment of RLS/WED, following treatment failure with dopamine agonists. Recent guidelines have taken these new data into account and highlight that a low dose of an opioid (prolonged-release oxycodone or methadone) may be considered in patients with very severe augmentation of symptoms. Alternative non-dopaminergic treatment concepts based on glutamatergic and adenosinergic mechanisms are currently in development, and are likely to provide encouraging therapeutic alternatives.

Reduced response to gabapentin enacarbil in restless legs syndrome following long-term dopaminergic treatment.

OBJECTIVES: To determine whether long-term treatment with dopaminergic agents (DAs) might dampen the response to a non-dopaminergic agent, such as gabapentin enacarbil. METHODS: We performed a two-week randomized, double-blind, crossover, and placebo-controlled study in a single, referral center in dopamine treatment-naive patients and non-augmented patients continuously treated with dopaminergics for the last five consecutive years. Following washout from any previous CNS-active drugs, patients were randomized into one of two groups for two consecutive two-week treatment periods with gabapentin enacarbil (GBPen) and placebo. Treatment was administered at 7 PM at a fixed dose of 600 mg/day. RLS severity was measured weekly using the International RLS Scale (IRLS) and Clinical Global Improvement (CGI). An M-SIT was also performed between 6 pm and midnight at the end of each treatment condition. RESULTS: There were no significant differences between groups in age, sex, duration of disease, ferritin levels, RLS severity at baseline, or existing concomitant conditions. Both groups improved more during treatment with GBPen than during placebo on the IRLS scale, CGI and mSIT. However, improvements were greater in the DA-naïve group than in long-term treatment with DAs group on the IRLS (p < 0.05), CGI (p < 0.01), and mSIT (p < 0.01). CONCLUSIONS: Previous long-term treatment with DAs reduces future response to GBPen in RLS patients. Potential pathiophysiological explanations are discussed. Our finding has strong implications for the initial choice of treatment in RLS and supports the notion that initial treatment should not be started with DAs. CLASSIFICATION OF EVIDENCE: The study provides class II evidence supporting reduced effects of gabapentin enacarbil in RLS patients previously exposed to long-term treatment with dopamine agonists.