Efficacy of l-Arginine treatment in patients with HTLV-1-associated neurological disease

Abstract

Objective: HTLV-1 infection causes HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP), resulting in loss of motor function. In this Phase 2 trial, we assessed the efficacy and safety of l-arginine in patients with HAM/TSP. Methods: This open-label, single-arm, Phase 2 study enrolled patients diagnosed with HAM/TSP. Patients received l-arginine at a dose of 20 g orally for 1 week and were followed-up for 3 weeks. The primary endpoint was change in walking speed in the 10-m walk test (10MWT). The main secondary endpoints were change in Timed Up and Go Test (TUGT) time, improvement in inflammatory markers in cerebrospinal fluid (CSF), safety, and tolerability. Results: The study enrolled 20 patients (13 [65%] female) with a mean age of 67.8 years (95% CI 62.3 to 73.3). Although the primary endpoint, the changes in 10MWT time between baseline (Day 0) and Day 7, did not reach statistical significance (mean percent change in time −3.5%, 95% CI −10.8% to 3.7%; P = 0.32), a significant improvement was detected between baseline and Day 14 (−9.4%, 95% CI −16.6% to −2.2%; P = 0.01). Significant improvements were also observed in selected secondary endpoints, including in TUGT time (−9.1%, 95% CI −15.5% to −2.7%; P < 0.01), and in neopterin concentration in CSF (−2.1 pmol/mL, 95% CI −3.8 to −0.5; P = 0.01). Adverse events were infrequent, mild, and resolved rapidly. Interpretation: l-arginine therapy improved motor function and decreased CSF inflammatory markers. l-arginine thus represents a promising therapeutic option for patients with HAM/TSP. Trial Registration Number: UMIN000023854.