Background: Spontaneous movement abnormalities, occurring independent of medication status, are thought to reflect basal ganglia pathology in patients at ultrahigh risk (UHR) for psychosis. To date, the research literature has primarily focused on movements associated with elevated striatal dopamine (i.e., hyperkinesia) while little is known about motor symptoms associated with low levels of subcortical dopamine (i.e., spontaneous parkinsonisms; SPs). As SPs (e.g., bradykinesia) may be governed by distinct neural mechanisms, this line of research can provide a clearer picture of the etiological processes in the prodrome. AIMS: To examine SPs and striatal structural correlates in youth at risk for psychosis.
Methods: A total of 81 (35 UHR, 46 healthy controls) adolescents were administered a structured clinical interview, structural MRI scan, and handwriting kinematic analysis capable of assessing SPs that are not detectable by traditional observer-based inventories.
Results: The UHR group exhibited significant decreased velocity scaling (indicative of SPs), t(79) = -2.65, P ≤ 0.01, as well as decreased ipsilateral t(68) = -3.16, P ≤ 0.001 and contralateral t(68) = -3.32, P ≤ 0.001 putamen volume compared with the healthy control group. Further, decreased velocity scaling was significantly associated with smaller ipsilateral putamen r(68) = 0.23, P ≤ 0.05, 95% confidence interval (CI) (-0.005, 0.44), left r(68) = 0.23, P ≤ 0.05, 95% CI (-0.005, 0.44) and right r(68) = 0.21, P ≤ 0.05, 95% CI (-0.03, 0.42) caudate volume, as well as increased positive r(79) = - 0.20, P = 0.05, 95% CI (-0.40, - 0.02) and negative r(79) = - 0.27, P ≤ 0.05, 95% CI (-0.46, -0.06) symptoms across the sample.
Conclusions: These findings represent the first evidence for hypokinetic movement abnormalities in the UHR period, indicating that pathophysiological processes in UHR patients may also involve hypodopaminergia. The results implicate a dopamine-induced imbalance contributing to frontal-subcortical circuit dysfunction in the psychosis prodrome.