Semmes Weinstein Monofilament Test
What It Measures
Semmes-Weinstein monofilaments find the lightest touch a person can feel. A set of nylon filaments of increasing thickness is pressed against the skin until each bows, and because a given filament always bends at the same force, the one a person can just detect gives a repeatable threshold.
Testing runs with vision blocked, the hand or foot supported, and the filament held perpendicular for about a second and a half. The examiner works from thinner filaments to thicker, and the person says only when they feel something, not where. Thresholds fall into bands: normal light touch, diminished light touch, diminished protective sensation, loss of protective sensation, and deep pressure sensation only.
Further Reading
Additional Notes
Licensing Notes: The method is not proprietary and no license applies — must purchase the filament kit. Various manufacturers produce sets; the full 20-filament series and the reduced 5- or 6-filament clinical kits are both available.
Learn More: Filament numbers are logarithmic, not linear: the marking is the log of the force in milligrams, so 4.31 is 2 grams and 5.07 is 10 grams, not a proportional step. The standard bands are 2.83 (0.07g) normal, 3.61 (0.4g) diminished light touch, 4.31 (2g) diminished protective sensation, 4.56 or 4.60 (4g) loss of protective sensation, 5.07 (10g) further loss, and 6.65 (300g) deep pressure only. Filament handles are colour-coded to those bands, which is what makes mapping results onto a hand diagram practical.
