Researchers at the Department of Nuclear Medicine, University of Munich, investigated a method to predict which ADHD patients will not respond to Ritalin therapy by measuring the degree to which [Tc?99m]TRODAT-1, a radiolabled protein, binds to the dopamine transporter. The study used single photon emission computed tomography (SPECT) to quantify the degree of binding. They delivered the results of their study on June 22 at the Society of Nuclear Medicine's 51st Annual Meeting in Philadelphia.
Ritalin works by blocking the dopamine transporter, increasing dopamine levels in the brain. But this treatment is often controversial because it can involve long-term drug therapy in children. Because 20%–30% of patients with ADHD do not respond to Ritalin therapy, a method of predicting therapeutic response would reduce exposure of ADHD patients to a drug that is unlikely to be effective.
Initial symptoms and post-therapy symptoms were measured in 18 adult ADHD patients using the Clinical Global Impressions (CGI) scale. Of the 13 patients who showed high levels of dopamine transporter binding, 12 demonstrated a significant improvement of ADHD symptoms on Ritalin. Conversely, none of the 5 patients who showed reduced levels of dopamine transporter binding responded to Ritalin therapy.
According to Dr. Christian la Fougère, the presenting author of the study, "Our results indicate that measurement of dopamine transporter may be an important prognostic predictor for therapeutic response to Ritalin."
Dr. la Fougère went on to speculate, "If we can determine who will respond to the drug and who will not respond, then only those patients who will benefit will be treated with Ritalin. Moreover, we can begin to examine alternative methods to treat the ADHD patients who do not respond to Ritalin."
The Society of Nuclear Medicine is holding its 51st Annual Meeting June 19–23, 2004, at the Pennsylvania Convention Center in downtown Philadelphia. Hot topics for the 2004 meeting include techniques for the early diagnosis of Alzheimer's disease; advanced imaging for the diagnosis, staging, and treatment of cancer; nuclear cardiology; and the collaboration between nuclear medicine and bioengineering in the fight against cancer.