Nonmotor Symptoms Differ Between Essential Tremor and Tremor-Dominant Parkinson's Disease

Distinguishing between essential tremor (ET) and tremor-dominant Parkinson's disease (PD-TD) can be challenging due to overlapping motor symptoms. This study aims to investigate the differences in nonmotor symptoms (NMS) between ET and PD-TD patients to provide additional evidence for differentiating these two conditions.

This retrospective study included 1656 participants, comprising 558 PD-TD patients, 584 ET patients, and 514 controls. ET patients were assessed using the Tremor Research Group Essential Tremor Rating Assessment Scale (TETRAS), while PD-TD patients were evaluated based on the Unified Parkinson's Disease Rating Scale (UPDRS). All participants were assessed for NMS using the Nonmotor Symptoms Scale (NMSS).

The composite NMSS score for the PD-TD group was significantly higher than that for the ET group and the control group (23.44 ± 20.20 vs. 12.60 ± 14.89 vs. 9.37 ± 12.44, p < 0.001). Compared to ET patients, PD-TD patients had an increased risk of all NMS, especially in hyposmia (OR = 7.70, 95% CI: 5.11-11.62). The NMSS score, urinary symptoms, and hyposmia may play a role in differentiating ET from PD-TD. The area under the curve (AUC) is 0.766 (95% CI: 0.739-0.793), with a sensitivity of 80.8% and specificity of 58.6%. When family history is included in the analysis, the AUC increases to 0.819 (95% CI: 0.795-0.843), with sensitivity improving to 82.4% and specificity to 68.2%.

The study reveals significant differences in NMS between ET and PD-TD. Compared to patients with ET, those with PD-TD exhibit more frequent and severe NMS. NMS and family history are helpful in differentiating between ET and PD-TD.