Objective: Tc-99m TRODAT-1 has high affinity and specifity as an agent for presynaptic DAT in the striatum dopamine nerve terminal. Effectivity of Tc-99m TRODAT-1 for qualifying DAT in striatum was assessed in many of those studies published in the past. Although some studies found increase of DAT receptor attachment in patients with attention deficit hyperactivity disorder (ADHD) compared to the normal controls, some of them did not find any significant increase. Methylphenidate as first line treatment of ADHD blockades DAT receptors strongly. In Tc-99m TRODAT-1 brain SPECT studies, some patients had more frequent DAT attachment compared to the controls. The aim of this study is to assess Tc-99m TRODAT-1 brain SPECT changes in adolescents with ADHD after 2 months methylphenidate (MPH) therapy.
Method: Eighteen adolescents aged between 13-18 years, diagnosed with ADHD participated in the study. None of them had comorbid neurological disease or psychiatric disorders other than oppositional defiant disorder. All patients were right handed. ADHD diagnoses were made by two experienced child psychiatrists, based on ADHD criteria listed in the 4th edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR). For inclusion of the patients in this study, K-SADS-PL semi-structured clinical interview was carried out and confirmed ADHD diagnosis as well as CGI-ADHD-severity scale score >=3 at visit 1 were compulsory. DuPaul ADHD Questionnaire and Conner’s Teacher Rating Scale-Short Form were used. OROS-Methylphenidate treatment was applied orally on daily basis. After the baseline SPECT scan, each subject’s dose was individually titrated in accordance with the clinical response in CGI-ADHD-severity scale (DuPaul, 1991). OROS-MPH starting dose was 18 mg and within 4 weeks, it was titrated up to 54-72 mg (average dose is 1 mg/kg/day). Tc-99m TRODAT-1 was obtained by the Institute of Nuclear Energy Research (INER-Taipei, Taiwan). Regions of interest (ROIs) were drawn on the right basal ganglia, left basal ganglia and the localization of cerebellum as the background. The two consecutive transverse slices showing the highest uptake in the basal ganglia were selected. Mean counts per pixel were used. While comparing cerebellar activity, mean corrected activity in the basal ganglia was calculated as follows: (basal ganglia-background)/background. Pre-treatment and post-treatment results of clinical parameters and striatal DAT density in patients diagnosed with ADHD were compared analysis of Wilcoxon test.
Results: There was a statistically significant decrease in pre-treatment availability of DAT assessed by brain SPECT and after 2 months MPH treatment in both right and left basal ganglia (pre; 1.23±0.29 and post; 0.49±0.36, p=0.000, for right, pre; 1.15±0.27 and post; 0.49±0.35, p=0.000 for left). The mean score on the CGI was 5.1±0.6 (range: 4-6) at baseline, 3.4±1.0 (range: 2-5) at the second visit (p=0.000 for visit 1-2). Also, there was a statistically significant improvement in behavior at the second visit, as indicated by the scores in DuPaul and Conner’s Rating scales.
Conclusion: The decreased availability of DAT in basal ganglia under treatment with MPH correlates well with the improvement in clinical parameter in conformance to the findings of previous studies.