Essential Tremor and Digital Biomarkers: A Scoping Review Using the TRACE Framework to Map Readiness for Clinical Trials and Routine Practice

Background: Essential Tremor (ET) is the most prevalent movement disorder in adults yet remains underrepresented in digital biomarker research. As therapies evolve, the absence of validated digital endpoints represents a growing translational gap. We introduce TRACE (Technology Readiness And Clinical Evidence), a novel five-tier validation maturity framework, and apply it in a scoping review of the ET digital biomarker literature.

Methods: A PRISMA-ScR scoping review was conducted across four databases (2000–2025). Studies were eligible if they reported quantitative digital tremor measurement in ten or more ET participants. Each study was assigned to the highest satisfied TRACE tier: technical verification (T1), referenced clinical validity (T2), ambulatory and longitudinal utility (T3), clinical trial readiness (T4), or economic and implementation readiness (T5).

Results: One hundred and sixty-five studies were included: wearable inertial measurement units (n = 114), digitised handwriting (n = 16), computer vision (n = 15), surface EMG (n = 10), voice (n = 6), and gait (n = 4). One hundred and fifty-four (93%) were T2; nine T3; two T4, both deploying the Cala Health TAPS wristband; none T5. Home or ambulatory deployment was present in 13 studies, minimum detectable change data in three, and patient-reported outcome correlation in 11.

Discussion: Only 11 studies across two modalities were classified beyond T2, demonstrating ambulatory or longitudinal evidence beyond supervised clinical validation; the TAPS wristband is the sole platform to achieve Tier 4. Home deployment, minimum detectable change derivation anchored to patient experience, and patient-reported outcome integration remain key prerequisites before digital tremor metrics can function as trial endpoints or inform routine practice.

Highlights: Despite rapid advances in digital outcome measures for Parkinson’s disease, essential tremor remains largely overlooked. Reviewing 165 studies across six sensing modalities, we introduce TRACE, a five-tier validation framework, and find that while 93% of devices demonstrate basic clinical validity, only two achieve clinical trial readiness.