Objective identification of upper limb tremor in multiple sclerosis using a wrist-worn motion sensor: establishing validity and reliability

Introduction
Over 25% of people with multiple sclerosis experience tremor, which may impact on activities of daily living and quality of life. Yet there is no method to objectively measure tremor and effectiveness of interventions on tremor. This study aimed to test validity and reliability of a new objective measurement for upper limb tremor in people with multiple sclerosis.

Method
Twelve participants with multiple sclerosis who self-reported tremor were observed performing standardised tasks. Validity and reliability of a new method to detect tremor from wrist movement was established against occupational therapist observation of tremor (FAHN). Concurrent validity of severity (displacement) of tremor was assessed. Responsiveness to change in tremor characteristics was explored in a sub-set of participants using weighted wrist-cuffs.

Results
The new method correctly predicted 98.2% of tremor cases identified by the occupational therapist, with high sensitivity (0.988) and specificity (0.976). Calculated displacement of tremor correlated with FAHN tremor severity scores moderately (rs¿=¿.452, p¿=¿.004). The new measure was responsive to changes in tremor characteristics due to change in weight of wrist-cuffs.

Conclusion
The new method of characterising tremor in those with multiple sclerosis demonstrated excellent validity and reliability in relation to tremor identified by an occupational therapist, and could provide valuable objective insight into the efficacy of interventions.