Affordable Assessment of Parkinsonian and Essential Tremor: Diagnostic Spectrum, Uncertain References, and the Cost of Deferring a Decision

Abstract Accessible tremor measurements can support clinical assessment, but a binary distinction between Parkinson disease and essential tremor excludes important presentations and can encourage unwarranted certainty. This article develops a reproducible hypothetical analysis of diagnostic spectrum, selective deferral, reference error, and patient payments. A population of 1,000 assessments contains 300 people with Parkinson disease, 500 with essential tremor, and 200 with other presentations. A binary rule with 85% sensitivity and 15% false-positive rate in essential tremor appears 85% accurate when only those two groups are evaluated. Including an additional group with a 40% positive rate lowers accuracy to 80% and positive predictive value from 77.27% to 62.20%. An alternative rule defers 230 uncertain cases to clinical review. Accuracy among its 770 automatically classified cases is 88.44%, while automatic coverage is 77%; these quantities must be reported together. Referring both positive and deferred cases increases review demand from 410 to 511 and increases the number of people with Parkinson disease reaching review from 255 to 276. Under invented resource costs, the increase is 6,060 units, or 288.57 units per additional reference-positive person referred, without establishing cost effectiveness. A separate conditional-independence calculation shows that an imperfect reference can make an 85%-sensitive rule appear 77.79% sensitive. Contemporary smartphone and wearable studies motivate accessible measurement, while clinical classification and pathology studies justify preserving diagnostic uncertainty. The analysis supports a spectrum-aware pathway that measures coverage, errors, follow-up, and patient charges separately. It does not validate a tremor device, establish treatment benefit, or imply that a normal digital result should block clinically indicated assessment. 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