Semmes-Weinstein test

The Semmes-Weinstein test—also known as the monofilament test—is a way to assess the pressure sensitivity (sensibility) of the skin. By pressing on the skin with a thinner or thicker filament, the doctor or physiotherapist gains an idea of the patient's sensation at that spot.

What is it?

The test was developed by Josephine Semmes and Sidney Weinstein in 1960. They were two American doctors specialised in nerve research. The Semmes-Weinstein test kit consists of a set of monofilaments, filaments of different thicknesses.

Thicker filaments are stiffer and require more force to bend than thinner ones. The filaments are pressed against the patient's skin to test pressure sensitivity. The patient indicates whether and when they feel the pressure. This test is often applied to the hands and feet in people with brain or nerve injury. In this way, recovery of nerve function can be measured.

How do you use the Semmes-Weinstein test?

The Semmes-Weinstein test is based on the amount of force needed to bend the chosen filament into a C-shape. The test starts with a thin filament and then proceeds with increasingly thicker filaments. The moment the patient feels a filament, the test is finished.

During the test, it is important that the patient can concentrate fully. There should be no distraction, fatigue, or concentration problems, because these negatively affect the test result.

The test goes as follows:

• The hand or foot lies in a comfortable, relaxed position.
• The patient's sight is blocked so they cannot see the touch.
• First, the palm or sole is tested. If necessary, the back of the hand or foot is tested afterwards.
• The filament is placed perpendicularly on the skin with increasing pressure, without sliding over the skin.
• This pressure builds up over 1.5 seconds until a C-shape forms in the filament. The pressure is then maintained for 1.5 seconds and reduced again over 1.5 seconds.
• If the patient feels nothing, the test is repeated with a thicker filament.
• The thin filaments are tested 3 times in a row. The thick ones only once.
• To map out where the sensory problem is, the test starts at the tips of the fingers or toes and then moves further and further towards the wrist or ankle.
• The test result is recorded.

What does the test result mean?

The test has five possible outcomes:

1. Normal; there are no abnormalities.
2. Reduced sensation of light touch.
3. Reduced protective sensation (protection against damage). Potentially harmful stimuli are not perceived properly.
4. Complete loss of protective sensation. The patient does not feel potentially harmful stimuli. For example, in a spinal cord injury, in which the spinal cord is completely severed.
5. The test cannot be performed. For example, because the patient cannot concentrate.

The test is repeated regularly to measure improvement or deterioration. This can be every week in problems that improve or worsen quickly, or every 4-6 weeks.

When no further change is observed, or normal sensation has returned, further testing is not useful. In this way, the doctor or physiotherapist monitors whether a nerve, after an injury, condition, or operation, is recovering or not. Based on the result, it is determined whether further treatment is necessary.