Uncrossed Asymmetry in Pattern Visual Evoked Potentials: A Reappraisal.

PURPOSE: To demonstrate the utility of an uncrossed asymmetry in full-field pattern reversal visual evoked potentials (FF-PVEPs) will accurately predict a retrochiasmal lesion confirmed by MRI. METHODS: During an 8-year period, 754 patients had FF-PVEPs performed and analyzed without knowledge of their clinical histories and imaging studies. Interhemispheric amplitude ratios were calculated between N75-P100 and P100-N145 and deemed significant if both demonstrated greater than 50% amplitude asymmetry no matter which eye was stimulated (uncrossed symmetry). RESULTS: We identified 11 patients of 754 patients evaluated for 8 years (1.5%) whose FF-PVEP fulfilled our amplitude criteria. Ten of 11 had retrochiasmal lesions confirmed with MRI for a calculated positive predictive value of 91%. CONCLUSIONS: These data provide initial support for the hypothesis that specified amplitude criteria in FF-PVEPs can provide evidence for a retrochiasmal lesion. An abnormal interhemispheric amplitude ratio in FF-PVEPs is underrecognized as a diagnostic criterion for retrochiasmal lesion prediction.

Correlation between preoperative Kimura inching studies and intraoperative findings during endoscopic-assisted decompression of the ulnar nerve at the elbow.

BACKGROUND: During the evolution of the senior author's technique of ulnar nerve transposition to in situ decompression for ulnar neuropathy at the elbow, nerve conduction studies (NCS) including the Kimura inching method were performed preoperatively in an effort to ensure that all potential sites of compression were investigated intraoperatively. The purpose of this study is to compare the results of the Kimura inching technique with the intraoperative findings noted during decompression of the ulnar nerve at the elbow. METHODS: The medical records of consecutive patients who underwent in situ decompression of their ulnar nerves combined with endoscopic examination between March and December of 2009 were retrospectively reviewed. The site of ulnar nerve compression noted using the Kimura inching technique was compared with the intraoperative findings. RESULTS: Twelve consecutive patients (four with bilateral symptoms) underwent endoscopic ulnar nerve compression in the study period for a total of 16 cases analyzed. In 12 cases, the Kimura method localized the site of compression to Osborne's bands and/or the aponeurosis of the flexor carpi ulnaris (FCU). Intraoperatively, compression was noted at Osborne's bands, the FCU aponeurosis, and/or the FCU) muscle proper in all 16 patients. There was partial or full correlation between the nerve conduction data and intraoperative findings in 13/16 cases. CONCLUSIONS: There was good but not perfect agreement between the NCS and intraoperative findings, perhaps because transcutaneous NCS are less accurate when a nerve is surrounded by muscle. The information obtained in this study is valuable when planning surgery to address ulnar nerve compression.

Prolonged compound muscle action potential duration in critical illness myopathy: report of nine cases.

The objective of this study was to determine the diagnostic use of compound muscle action potential duration in patients with critical illness myopathy. Accurate diagnosis is important because the muscles recover once the offending agents are withdrawn. We retrospectively reviewed 9 cases seen at our institution between 1999 and 2003 in which critical illness myopathy was diagnosed on the basis of clinical and electrophysiological evaluations. All the patients had weakness, difficulty weaning from mechanical ventilation, sepsis, and exposure to intravenous corticosteroids in the intensive-care unit. Seventy-five percent of tested motor nerves had responses. Amplitude was decreased in 100% of ulnar and peroneal nerves, and 71% of median and tibial nerves. Duration was prolonged in 100% of responsive motor nerves. Prolonged compound muscle action potential duration was the most characteristic electrophysiological finding of critical illness myopathy. Its recognition as part of a quick and simple bedside diagnostic test makes it preferable to other tests.