A Useful Electrophysiologic Test For Diagnosis Of Minimal Conduction Block
The concept of motor nerve conduction block has gained more importance with the identification of new disease entities. In fact, the presence of motor conduction block greatly influences the diagnostic and therapeutical approach of neuropathies. In spite of the generally good sensitivity of the conventional nerve conduction evaluation, normal findings are still observed in a number of patients with clinical data strongly suggesting the presence of conduction block. We have developed a simple technique for the detection of conduction block by using SFEMG electrode. This test is based on the concept that from stimulation proximal and distal to a partial conduction block, several registrations from few muscle fibers could show some “blocked” fibers (innervated by “blocked” axons). To evaluate the usefulness, sensitivity and specificity of a new neurophysiological test for partial conduction block we studied 17 patients (17 nerves) with clinical picture strongly suggesting the presence of motor conduction block and 20 healthy subjects (40 nerves). Motor nerve conduction studies were performed with conventional surface technique and with the new technique we developed. Moreover, we also evaluated patients with other neurological diseases. According to recent AAEM consensus criteria, 5/17 cases presented “definite” partial conduction block and 6 presented “probable” partial conduction block. In contrast, 16/17 cases (94%) presented an evidence of conduction block at SFEMG conduction block test. The 5/6 cases that were not filled in the AAEM criteria and that presented abnormal findings at SFEMG nerve conduction test could be considered affected by “minimal conduction block.” The sensitivity of this new test was greater than the conventional test. The specificity was 100% (no abnormal findings in healthy subjects or patients with other diseases than neuropathy). SFEMG conduction block test is a sensitive, complementary technique for diagnosis of minimal conduction block in patients with normal findings in standard nerve conduction studies.
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Document Type: Abstract
Affiliations: Institute of Neurology, Università Cattolica, Roma
Publication date: March 1, 2001