Archimedes Spiral Looping in Functional and Essential Tremor

Area of Science:

• Neurology
• Movement Disorders

Background:

• Functional tremor (FT) is a common functional movement disorder with diagnostic challenges.
• Archimedes spiral drawings are a bedside tool for tremor assessment.
• The 'stretch slinky' sign (looping) is noted in FT, but its prevalence in FT versus essential tremor (ET) is unknown.

Purpose of the Study:

• To determine the prevalence of looping in Archimedes spirals for FT and ET.
• To assess the diagnostic utility of loop counts in differentiating FT from ET.

Main Methods:

• Retrospective analysis of Archimedes spirals from 22 FT patients and 28 ET patients.
• Quantification of loop counts in spiral drawings.
• Statistical analysis including Mann-Whitney U test and ROC analysis.

Main Results:

• Looping (≥1) was present in 45.5% of FT spirals and 60.7% of ET spirals.
• No significant difference in loop counts between FT and ET groups.
• A loop count threshold of ≥7 showed high specificity (0.96) but low sensitivity (0.14) for FT (PPV 0.75).
• ROC analysis yielded an AUC of 0.46, indicating poor discriminative ability of loop counts alone.

Conclusions:

• Archimedes spiral looping occurs in both FT and ET.
• Loop counts alone have limited ability to distinguish between FT and ET.
• A loop count ≥7 may be a specific, though insensitive, indicator for FT within a broader clinical evaluation.