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Neurology India, Vol. 55, No. 2, April-June, 2007, pp. 103-104 Invited Commentaries Electrodiagnostic studies in ulnar neuropathy at the elbow Visser LeoH Department of Neurology and Clinical Neurophysiology, St. Elisabeth Hospital, PO Box - 90151, 5000 LC Tilburg, The Netherlands Code Number: ni07043 The clinical spectrum of ulnar neuropathy at the elbow (UNE) ranges from intermittent paresthesias in the fourth and fifth digits to complete sensory loss in the area of the ulnar nerve with atrophy and weakness of the ulnar muscles. Electrodiagnostic studies are usually applied to confirm the diagnosis. In 1999 the American Association of Electrodiagnostic Medicine (AAEM) made several recommendations to optimize the electrodiagnostic protocol for UNE.[1] The authors obtained normal values of the motor ulnar nerve conduction velocity (NCV) recording from the first dorsal interosseus (FDI) and the abductor digiti minimi (ADM) muscle. The study was performed in 50 healthy controls. The normal values of the motor NCVs differed between the recordings from the ADM and FDI. Mainly the NCVs of the right ulnar nerve recording from the FDI showed lower normal values in comparison to the other measurements. The authors concluded that by taking the normal values of ADM while recording from the FDI could lead to false-positive diagnosis.[2] It emphasizes that it is important to have adequate normal values of each separate test. There is much debate over which muscle to record from the evaluation of UNE.[2] Two recent studies indicate that the sensitivity for detecting the motor conduction block or slowing across the elbow in patients with UNE was similar for ADM and FDI recording, but recording from both muscles may increase yield.[2],[3] However, applying two motor studies may artificially increase the diagnostic yield on statistical grounds when only one of the tests needs to be abnormal to make the diagnosis. A disproportional slower motor NCV across the elbow in comparison to the velocity of an adjacent nerve segment has probably only little or no additional value.[2],[3] The diagnosis of UNE is straightforward when motor NC studies show a conduction block across the elbow. However, in many patients the only localizing electrodiagnostic abnormality is motor NCV slowing across the elbow. Unfortunately, the 95% confidence interval of the mean motor NCV across the elbow may vary considerably due to accumulation of distance and latency measurement errors[4] and therefore, isolated differential slowing across the elbow is anyway of limited value as a sole criterion. Furthermore, routine NCS cannot discriminate between a lesion at the retroepicondylar groove and the humero-ulnar arcade. Precise localization by using inching may then be of additional use.[5] References
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