Archimedes Spiral Ratings: Determinants and Population-Based Limits of Normal.

Background: Tremor is commonly found among healthy humans or prevalently a symptom of neurological dysfunctions. However, the distinction between physiological and pathological tremor is dependent on the examiner's competence. Archimedes Spiral Rating (ASR) is a valid and reproducible semi-quantitative method to assess the severity of action tremor.

Objectives: (1) To assess the range and percentiles of ASR in a large sample seemingly free of tremor-related conditions or symptoms from the population-based CHRIS-study. (2) To analyze the influence of sex, age, and the drawing hand on ASR. (3) To define ASR limits of normal. (4) To supply exemplary Archimedes spiral drawings by each rating to favor consistent and proficient clinical evaluation.

Methods: Accurately investigated participants were randomly sampled over 14 sex-age strata. 2686 paired spirals drawn with both hands by 1343 participants were expertly assessed on a tremor rating scale from 0 to 9.

Results: ASR had a quadratic increase with age in both sexes, while it was relatively lower in the dominant compared to the non-dominant hand and in women compared to men. ASRs above sex-age specific 97.5th percentiles of 4 and 5, below and above 60 years of age, respectively, were conceivably of non-physiological nature.

Conclusions: In a large population-based sample we show a steeper increase of action tremor by age as age progresses. Relatively higher ratings among the elderly, males and the non-dominant hands, appear compatible with ASR limits of "normal" across sex-age groups. The current operational evidence may support practitioners differentiating physiological and pathological hand tremor.