Tuning Fork Excels in Diabetic Neuropathy Dx
The increased sensitivity of the CTF comes at the expense of specificity, however, identifying many at-risk patients who would not end up developing an ulcer if left untreated. Specificity of the CTF is just 20%, compared with 75% for the monofilament. “If you want to prevent ulcers, you have to identify everyone at risk, so you can do everything you can to prevent them, with measures such as teaching patients to use mirrors to inspect their feet, and in some cases provide custom footwear,” he noted.
But Dr. Andrew J.M. Boulton, chair of the ADA'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 “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. In one review of six such studies, the increased risk of ulceration ranged from an odds ratio of 2.2 to 9.99, and the relative risk of amputation was 2.9 with an abnormal monofilament test (J. Fam. Pract. 2000;49[11 suppl]:S17-29).
“What is needed with this test is a prospective study…. This new tuning fork test may well be useful but before it can replace the monofilament—if it is to at all—good longitudinal studies must be done to show its predictive value,” said Dr. Boulton, who has received honoraria/consulting fees from Pfizer and Eli Lilly & Co.
Dr. Oyer and Dr. Saxon are conducting two ongoing trials with the CTF test. One is seeking to establish vibration perception ranges for nondiabetic people aged 40 and older. The other is looking at whether Metanx, a widely-used vitamin therapy for diabetic neuropathy, improves the CTF score, he said in an interview.
Dr. Oyer and Dr. Saxon stated they had no conflicts of interest to disclose.
Although the method takes some practice, the clanging tuning fork test is simple and reliable, Dr. Saxon said, using these steps:
▸ Using a standard C-128 tuning fork, strike the tuning fork against the palm with an upstroke, just hard enough to make the ends clang together. If there is no metallic “clang,” try hitting harder. But if there is an extra-loud “clang,” dampen it and try again more lightly.
▸ Hold the tuning fork with only two fingers. “Pretend you're at a bar holding a dart,” Dr. Saxon said. Don't rest your hand against the tines because contact will shorten the vibration time.
▸ When using the CTF on patients for the first time, it's a good idea to demonstrate on one of their hands to make sure they understand the difference between vibration and pressure by checking if they recognize when the vibration stops.
▸ For the actual test on the foot, immediately after striking, the tuning fork is placed on the dorsal toe just proximal to the nail, and the seconds counted until the patient says “now,” signifying the point at which he or she begins to doubt that the vibration is perceptible.
▸ The test is repeated on the other foot, and the score from both toes is averaged.
