The Amygdala's Neurochemical Ratios after 12 Weeks Administration of 20 mg Long-acting Methylphenidate in Children with Attention Deficit and Hyperactivity Disorder: A Pilot Study Using (1)H Magnetic Resonance Spectroscopy

OBJECTIVE: Recent pediatric studies have suggested a correlation between decreased amygdala volume and attention deficit and hyperactivity disorder (ADHD) symptoms, including the emotional dysregulation. To investigate the hypothesis that medication treatment of ADHD specifically improves amygdala function, we used (1)H magnetic resonance spectroscopy (MRS) to study the effect of 12 weeks of treatment with daily 20 mg long-acting methylphenidate on the Glu/Cr, NAA/Cr, Cho/Cr, and mI/Cr ratios in the amygdala of medication-naïve children with ADHD. METHODS: This was a prospective study, using a pre- and post-test design, on a single group of 21 children (average age 8.52 years, 17 males and 4 females) diagnosed with ADHD. Low Time Echo MRS scans sampled voxels of interest (1.5×1.5×2.0) from both the right and left amygdala. RESULTS: There was significant clinical improvement after 12 weeks of treatment with 20 mg long-acting methylphenidate. On 1H MRS, there were no statistical significant differences of NAA/Cr ratio, Cho/Cr ratio, mI/Cr ratio before and after 12 weeks administration of 20 mg long-acting methylphenidate both in the right and left amygdala. In addition, Glu/Cr ratio decreased 14.1% in the right amygdala (p=0.029) and 11.4% in the left amygdala (p=0.008). Standardized mean effect sizes ranged from 0.14-0.32. CONCLUSION: The findings are consistent with the possibility that hyperglutamatergic processes in the amygdale are related to the hyperactive-impulsive symptoms of ADHD.