Non-motor symptoms are widely recognised in both Parkinson’s disease (PD) and essential tremor (ET). Clock-drawing (CD) tests appear to be impaired relatively early on during the progression of cognitive (executive) decline in PD.1 However, the optimal measures for detecting cognitive changes in patients with ET have not been established.2-4 This study examined whether the CD test could provide the opportunity to quickly predict visuospatial deficits in patients with ET.
METHOD AND RESULTS
Visuospatial performance was assessed in 58 consecutive patients with ET, 75 patients with PD, and 22 healthy controls (HC), all of whom had visited two specialised memory clinics in Athens, Greece. The ‘CD and copy’ (CC) tasks in the Parkinson’s Disease-Cognitive Rating Scale (PD-CRS) were used as a test of visuospatial function.
Both CD and CC scores were lower for patients with ET compared to those with PD and HC (p<0.001 for both comparisons). A binomial logistic regression showed that both CD and CC tasks could predict if participants had ET or PD with high sensitivity (94.7%), specificity (87.9%), and an area under the curve of 0.980 (95% confidence interval: 0.962–0.997). The model was able to explain 86.1% (Nagelkerke R2) of the variance in the disease variable (ET/PD) and correctly classified 91.7% of the cases.
These results showed for the first time that patients with ET have more frontal and visuospatial deficits compared to PD; similar previous studies have not shown this. In the study by Lombardi et al.,5 the patients with PD exhibited poorer performance in visuospatial tasks compared to ET. Moreover, Gasparini et al.6 reported that patients with PD performed worse in some verbal fluency and executive tasks than patients with ET. In the Benge et al.7 study, the 15 patients with PD displayed a poorer performance in executive function tests than the 11 patients with ET. The results are, however, in agreement with the Lombardi et al.5 functional MRI study which showed decreased functional connectivity in visual and frontoparietal network in patients with ET compared with those with HC. It could be speculated that these functional changes in ET may be an early marker of non-motor cognitive manifestations that are related to ET. However, additional studies are required before this hypothesis can be confirmed.
Patients with ET have more visuospatial deficits compared to those with PD. CD testing appears to be a robust predictor of ET, after adjustment for age and education. These findings suggest that the CD test may be an easy and useful tool to track cognitive changes in non-dementia patients with ET in clinical practice.