Atlanta — The clanging tuning fork test is far more accurate and sensitive than is the 10-g monofilament in screening diabetes patients for peripheral neuropathy, results from two studies suggest.
In fact, relying on the monofilament alone to screen patients for diabetic peripheral neuropathy (DPN) will miss all but the most severe, advanced cases, Dr. David S. Oyer and Dr. David Saxon said at the annual meeting of the American Association of Diabetes Educators.
But Dr. Andrew J.M. Boulton, chair of the American Diabetes Association's Foot Care Interest Group, said he believes that it's too soon to replace the monofilament with the CTF as a first-line screening test for diabetic neuropathy. The CTF results are “of course very interesting, and I think that this is certainly a useful addition to the monofilaments,” he said in an interview, adding that they are consistent with last year's recommendation of using monofilaments together with one other of four tests. Dr. Boulton, who divides his time between the Manchester (England) Diabetes Centre and the division of endocrinology, diabetes, and metabolism at the University of Miami, noted that data from prospective studies also support the monofilaments.
Dr. Oyer presented data from two studies, one of which showed that the 10-g Semmes-Weinstein monofilament test was normal in more than two-thirds of patients who were found by the CTF test to have severe DPN. Guidelines from the American Diabetes Association—endorsed by the American Association of Clinical Endocrinologists—recommend the 10-g monofilament as the main screening tool for diabetic foot evaluation, along with a choice of one of four other tests. (Diabetes Care 2008;31:1679-85).
Dr. Saxon, an endocrinology resident at the University of Michigan, Ann Arbor, enumerated several limitations of the monofilament, including the fact that those distributed free by drug companies often are not reliable and do not always give 10 g of force. Moreover, cold monofilaments must be warmed up to work properly. After about 100 bends, monofilaments tend to “fatigue” and need to “rest” for 24 hours. Also, testing on a callus can give an inaccurate result, Dr. Saxon said.
In a previously published study, Dr. Oyer demonstrated reproducibility of the CTF in 12 patients with diabetes on whom he performed the test 10 times on the same toe for each. Scores ranged from 3.4 to 18.8 seconds, with a mean of 10.2 and standard deviation of 1.3 seconds, representing less than a 10% error.
In a second part of that study, a single reading from the right foot versus the left foot was compared in 30 randomly selected patients with diabetes. The vibration duration sensation averaged was 10.9 seconds on the right foot and 9.7 seconds on the left, said Dr. Oyer, an endocrinologist at Northwestern University, Chicago.
Monofilament testing was done in patients whose mean vibration duration was 8 seconds or less, and was consistently reported as normal among the 26 patients who had vibration durations of 5 seconds or more. Only at vibration perceptions of 4 seconds or less did the monofilament testing begin to demonstrate abnormal results (Endocr. Pract. 2007;13:5-10).
Dr. Oyer and Dr. Saxon stated that they had no conflicts of interest to disclose.