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Education Material for Health Care Professionals: Newsletter Version

THE FEET AND DIABETES

Testing vibration sensation with a biothesiometer.



A probe is applied to part of the foot, usually on the big toe. The probe can be made to vibrate at increasing intensity by turning a dial. The person being tested indicates as soon as he/she can feel the vibration and the reading on the dial at that point is recorded. The biothesiometer can have a reading from 0 to 50 volts. The reading is low in young normal individuals (ie.they are very sensitive to vibration). As we get older, the biothesiometer reading becomes progressively higher. From experience, it is known that the risk of developing a neuropathic ulcer is much higher if a person has a biothesiometer reading greater than 30-40 volts, if the high reading cannot be explained by age.

In recent times, it is felt as much information can be obtained by the use of the monofilament test. Consequently, biothesiometry is rarely carried, or even required, in the vast majority of cases.

The use of the monofilament test is simple and gives a great deal of information and should be routinely carried out by any doctor treating patients with diabetes.



A standardized filament is pressed against part of the foot. When the filament bends, its tip is exerting a pressure of 10 grams (therefore this monofilament is often referred to as the 10gram monofilament). If the patient cannot feel the monofilament at certain specified sites on the foot, he/she has lost enough sensation to be at risk of developing a neuropathic ulcer. The monofilament has the advantage of being cheaper than a biothesiometer, but to get results which can be compared to others, the monofilament needs to be calibrated to make sure it is exerting a force of 10 grams.

Sensation threshold screening using a 10 gram monofilament (also known as Semmes-Weinstein monofilament).

  1. Use the 10g monofilament to test sensation.
  2. Show the patient the filament and touch it to his or her hand to show it does not hurt.
  3. The sites to be tested are indicated on the foot diagram below.
  4. Apply the filament perpendicular to the skin’s surface ( see Diagram A).
  5. The approach, skin contact and departure of the monofilament should be approximately 1.5 seconds duration.
  6. Apply sufficient force to allow the filament to bend ( see Diagram B).
  7. Tell the patient to say if he or she feels the filament. Do NOT ask “Do you feel this?”
  8. Do not allow the filament to slide across the skin or make repetitive contact at the test site.
  9. Touch the parts of the feet randomly.
  10. If the patient does not say “YES” at any point, go to another place and come back to this part again later.
  11. Do not apply to an ulcer site, callous , scar or necrotic tissue.

 Diagram A  
Diagram B  
The circles represent the places on the foot to test with the monofilament  
Consider  feet to be “at risk” if patient cannot feel the 10gm monofilament at any of the sites marked.  

If necessary, the following tests should be considered :

  • Nerve Conduction, and
  •  EMG studies.
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