Handwriting patterns in isolated rapid eye movement sleep behaviour disorder

Background Handwriting changes are recognised as an early manifestation of Parkinson's disease. Whilst isolated rapid eye movement sleep behaviour disorder (iRBD) is strongly associated with future Parkinson's diagnosis, changes in handwriting remain under-explored. Objective To assess the handwriting of people with iRBD and develop a rating scale for detection of early disease clinical hallmarks. Methods Cross-sectional study involving 33 people with polysomnography-confirmed iRBD and 29 controls. Participants copied a standard sentence using pen and paper. A graphologist analysed each script blindly and designed a scale based on observed abnormal patterns which included: micrographia, sentence slope, hidden tremor, retracing, resting marks, irregular shape, excessive pen pressure, and inconsistent word spacing. Each item was scored 0/1 based on their absence/presence. Separately, three blinded movement disorders experts assessed the scripts based on their global clinical impression as well as using the rating scale. Results People with iRBD were slower to complete the task than controls (76.70 s (SD = 30.39) vs 61 s (SD = 10.71); p = 0.004). Hidden tremor was the most common feature amongst the iRBD group (72.0% vs 34.5%; p = 0.005), followed by sentence slope (60% vs 24% p = 0.005) and pen pressure (48% vs 14%; p = 0.006). Micrographia was observed in both groups (iRBD 45.4%, controls 41.4% p = 0.801). Classification accuracy of the scale for iRBD was higher than expert global assessment (AUC 0.76 vs AUC 0.62; p = 0.029). Conclusions Writing speed, tremor, pen pressure and sentence slope are handwriting features that warrant further investigation to define early patterns in people with iRBD.