Tourette's syndrome: [I-123]β-CIT SPECT correlates of vocal tic severity

Objective: To examine in vivo the density of brain monoaminergic transporters in Tourette's syndrome (TS). Background: TS is a heritable neuropsychiatric disorder characterized by chronic vocal and motor tics and is often associated with obsessive-compulsive symptoms. Hyperstimulation of dopamine receptors and dysfunction of serotonergic transmission have been implicated in its pathogenesis, but direct evidence of involvement of these neurochemical systems has been limited. Methods: Symptom severity and the availability of presynaptic monoaminergic transporters in the basal ganglia, midbrain, and thalamus were measured using SPECT and the radioligand [I- 123]2β-carbomethoxy-3β-(4-iodophenyl)tropane ([I-123]β-CIT) in 10 patients with TS and in 10 age- and sex-matched normal volunteers. Results: A significant negative correlation was found between a measure of overall tic severity and β-CIT binding in the midbrain (r = -0.73, p = 0.02) and the thalamus (R = -0.82, p < 0.01). When examined post hoc, these correlations were determined largely by vocal tic severity. No other significant correlations were found between symptom severity and β-CIT binding in the striatum or cortex. Conclusions: These findings indicate that serotonergic neurotransmission in the midbrain and serotonergic or noradrenergic neurotransmission in the thalamus may be important factors in the expression of TS and may suggest novel targets for treatment.