Legend: SNAP = sensory nerve action potential Finally, to compare the sensitivity and specificity of the two tuning forks to each other, an extended McNemar’s test 8 was applied to determine whether there was a significant difference between the two tools. ![]() For example, if a patient had a TP reading by the Rydel – Seiffer tuning fork on both left and right sural nerve, this patient contributed two data points.įor both tuning forks, the following measures of diagnostic accuracy were then calculated: Sensitivity = TP/(TP + FN), Specificity = TN/(TN + FP), Positive Predictive Value = TP/(TP + FP), and Negative Predictive Value = TN/(TN+FN). True Negative (TN), True Positive (TP), False Negative (FN) and False Positives (FP) were calculated for the quantitative Rydel-Seiffer tuning fork and the qualitative 128 Hz tuning fork, as follows: TN was defined as normal tuning fork reading with normal sensory nerve action potentials (SNAPs) TP was defined as abnormal tuning fork reading with abnormal SNAPs FN was defined as normal tuning fork reading with abnormal SNAPs and FP was abnormal tuning fork reading with normal SNAPs.Įach of the median, ulnar and sural nerves was categorized separately, and data points for left and right of the same nerve also counted separately within the same category. We recorded sensation as abnormal if vibration was perceived on the corresponding joint of the examiner (for example, comparing the metatarsal joint vibration sensation of the patient to the same joint on the examiner), for a count of five seconds after patient reported cessation of sensation, thus increasing the specificity of the finding.įor the analysis, right or left sural nerve conduction data was correlated to the measurements of the two tuning forks at the corresponding metatarsal joint, and right or left median and ulnar nerve conduction data was correlated to the measurements at the corresponding distal interphalangeal joint. 1 These approaches compare proximal sensation to distal, which would overestimate abnormal values. Some have suggested placing the examiner’s finger on the opposite surface of the joint being tested from the tuning fork and noting if the vibration persists after the patient no longer senses it, 2 or assessing the patient’s threshold against the examiner’s, by applying the tuning fork to their finger. 3 For the qualitative 128 Hz tuning fork, absent sensation was categorized as abnormal, however, no uniform criteria has been described for decreased vibratory sensation. For the Rydel-Seiffer tuning fork, values ≤ 5 was categorized as abnormal at the distal interphalangeal joint on the second digit 7 values ≤ 4 was categorized as abnormal at the first metatarsal joint. The tuning forks were struck maximally and applied perpendicularly to the (a) dorsal head of the first metatarsal joint, and (b) distal inter-phalangeal joint on the second digit (index finger). Following training under board-certified neuromuscular physicians, the qualitative and quantitative tuning forks were tested in a consecutive fashion by neuromuscular fellows and medical students.
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