The value of the Rydel-Seiffer tuning fork as a predictor of diabetic polyneuropathy compared with a neurothesiometer

Aims The aim of the study was to investigate the predictive value of the Rydel-Seiffer tuning fork for detecting diabetic neuropathy and to compare it with an electronic neurothesiometer. Methods In 2022 consecutive diabetic subjects, peripheral polyneuropathy was diagnosed by vibration perception threshold (VPT) at the tip of both great toes using a 128-Hz tuning fork and a neurothesiometer, by simple bedside tests and by the presence of neuropathic symptoms. These evaluations were further combined to diagnose peripheral nerve dysfunction (abnormal bedside tests) and symptomatic neuropathy. VPT was also measured in 175 non-diabetic control subjects to define normal values. Results VPT was normal in 1917 subjects and abnormal in 105 (5.2%) patients when measured by the tuning fork. Patients with an abnormal vibration test were significantly (P < 0.0001) older than subjects with a normal vibration sense, while diabetes duration and HbA(1c) of the former were also significantly elevated. The same was true for the percentages of an abnormal 10-g monofilament test (66.7% vs. 7.2%, P < 0.0001) and a missing Achilles' tendon reflex (68.6% vs. 24.8%, P < 0.0001). Finally, the VPT measured by the neurothesiometer was 2.5 times higher in patients with an abnormal tuning fork test (32.0 +/- 9.8 vs. 12.5 +/- 6.4 V, P < 0.0001). The plot of the difference of both methods against their mean yielded a good agreement of the two VPT measurements, and the tuning fork had a high sensitivity and positive predictive value for the diagnosis of abnormal bedside tests and for symptomatic neuropathy. Conclusion The tuning fork reliably detected peripheral neuropathy in comparison with the neurothesiometer. A tuning fork is a useful screening test for diabetic neuropathy.