Single-photon emission computed tomography (SPECT) was used to monitor the dopamine transporter activity in 5 males, ages 8 to 10, with ADHD, after cessation of methylphenidate (MPH) treatment, in a study at the University Hospital Maastricht, The Netherlands. A reduction in dopamine transporter in the striatal system was observed at 3 months after initiation of treatment with MPH. After withdrawal of MPH for a minimum of 4 weeks, following prolonged treatment for 9 to 20 months, dopamine transporter activity had increased to pretreatment levels. Prolonged MPH treatment of ADHD does not cause any permanent modification of nigrostriatal dopaminergic pathways. 
COMMENT. In this small pilot study using SPECT, the reduction in dopamine transporter activity induced by MPH in the treatment of ADHD is shown to be reversible after withdrawal of the medication, and no permanent damage to the striatal system results when therapy is prolonged for up to 20 months. The dopamine transporter system appears to be a primary target for MPH in ADHD (Dresel S et al, 2000; Dougherty DD et al, 1999;cited by authors).