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.