Dopaminergic dysfunction and psychiatric symptoms in movement disorders: a 123I-FP-CIT study: reply to comment by Erro et al.

Dear Sir,We appreciate the interest of Erro and colleagues in our work and are grateful for their comments [1], giving us the opportunity to add further details and discuss the results of our study [2]. We also thank them for having brought to our attention their recently published article focusing on patients with newly diagnosed or untreated Parkinson’s disease (PD), which unfortunately had not been published at the time of our submission.The main objective of our study was not to address the relationship between asymmetry of motor signs and psychiatric symptoms in PD patients but to investigate a possible correlation between DAT availability and affective symptoms in the most common movement disorders, including for the first time patients with essential tremor and primary dystonia. We also included PD patients in order to contribute to the debate in the literature on the role of dopamine in PD-related affective symptoms, a subject on which several published studies have shown unclear results [3, 4]. However, Erro and colleagues raise this interesting issue of motor asymmetry, as they enrolled a sample of patients balanced for laterality of parkinsonian signs (17 patients for each group). By contrast, we enrolled 21 consecutive PD patients: 11 patients with left side predominant motor symptoms, 6 with right side predominant motor symptoms, and 4 with only mild asymmetry on the motor scale score (3 left side and 1 right side). We found an inverse significant correlation between depression symptom levels (evaluated by means of the Hamilton Depression Rating Scale) and DAT availability in the left caudate. This result is additionally strengthened by our unbalanced patient sample, as the majority of patients had a lower DAT availability on the right side, corresponding to the most affected hemisphere. By contrast, Erro and colleagues found a significant inverse correlation between anxiety levels (evaluated by means of the Hospital Anxiety Depression Scale, HADS, anxiety subscale, HADS-A) and DAT availability in the right caudate.Their findings stimulated an additional analysis of our data: in PD patients, Hamilton Anxiety Rating Scale (HARS) scores did not correlate with age (r = 0.18, p = 0.47), duration of disease (r = 0.39, p = 0.11), H&Y stage (r = 0.16, p = 0.52) or UPDRS III score (r = 0.11, p = 0.65). HARS scores did not correlate with DAT availability in the right and left caudate after controlling for these factors (partial correlation coefficients: right caudate r = −0.06, p = 0.80; left caudate r = −0.26, p = 0.29). In addition, while we did not find any correlation between anxiety levels and DAT availability in the bilateral caudate of the right side predominant motor group (n = 7), a trend towards a correlation between anxiety levels and DAT availability in both the right and the left caudate was detected in patients with left side predominant motor signs (n = 14; r = −0.48, p = 0.08, for both analyses). This result supports the importance of enrolling large patient samples also balanced for motor side involvement, as correctly stated by Erro and colleagues. Such balance could not have been achieved in our study due to its consecutive enrolment. The study by Erro and colleagues was instead a retrospective one.Two previous SPECT studies that used similar methods to ours [3, 4] did not include motor laterality in their analysis. However, in line with our results, both studies found an inverse correlation between affective symptoms and DAT availability in the left hemisphere. On the other hand, the correlation with the caudate nucleus does not necessarily reflect the predominance of motor signs on a hemibody over the opposite one, as it has been reported that motor signs mainly correlate with the uptake in the putamen [5]. Moreover, this trend of reasoning well explains why the literature on motor side onset and non-mot