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11.2. Methods to assess the foot at risk
11.2.1. Neuropathy
The studies of nerve conduction are considered the reference pattern to diagnose
peripheral neuropathy, but this technique is not available for generalized use.
A recent SR (247) has analysed the diagnose capacity of other simpler and
more accessible methods:
Monofilament
In three prospective studies, the monofilament identified patients with high ulceration
risk, with a sensitivity from 66% to 91% and a specificity from 34% to 86%, a
positive predictable value from 18% to 39% and a negative predictable value from
94% to 95% to predict the evolution to ulcer.
The test is carried out with the 5.07 SWM (10 g) monofilament pressing on
four plantar points in each foot: first toe (distal phalanx) and the base of the first,
third and fifth metatarsal (247; 248). The test is considered positive when there is
at least one insensitive point (248).
The monofilament cannot be used in more than 10 patients without a 24-hour
recovery period (247).
Appendix 8 describes the use of the monofilament.
Studies of
diagnostic
tests
II
Tuning fork
It is a simple and cheap method to measure vibratory sensation (247), though it
has reliability problems. It is less accurate as regards ulcer prediction (248) than
the monofilament. It can be used as an alternative if there is no monofilament
available.
Biotensiometer
The biotensiometer exceeds the reliability limitations of the tuning fork as it can
regulate the different vibration thresholds. A vibration threshold over 25V has
83% of sensitivity, 63% of specificity, a positive likelihood ratio (+LH) of 2.2 (CI
95%: 1.8-2.5), and negative likelihood ratio (-LH) of 0.27 (CI 95%: 0.14-0.48)
to predict foot ulcer after four years (247). This technique is not available on a
general basis within our field.
Studies of
diagnostic
tests
II
100 CLINICAL PRACTICE GUIDELINES IN THE NHS