A new, sensitive electrodiagnostic test for conduction block

The presence of neuroapraxic block greatly influences the diagnosis and therapeutic 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 neuroapraxic block. In 17 patients (17 nerves) with certain diagnosis of motor neuroapraxic block due to different pathologies (diagnosis was based on the clinical picture, the evolution, response to treatment and sural biopsy) and 20 healthy volunteers (40 nerves), motor nerve conduction studies were performed with standard surface technique and with a new technique that we have developed: the SFEMG nerve conduction test. To evaluate the specificity of the new test, we also evaluated 10 patients with other neurological diseases. Current AAEM criteria for partial conduction block were used for the standard conduction block tests. Five out of 17 cases presented "definite" partial conduction block and 6 presented "probable" partial conduction block. In contrast, by using the SFEMG recording, 16/17 cases (94%) presented evidence of conduction block at SFEMG nerve conduction test. The 5 out of the 6 cases who do not fulfilled the AAEM criteria and who 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 conventional tests. The specificity' was high (no abnormal findings in healthy subjects or patients with other diseases than neuropathy). The SFEMG nerve conduction test is a sensitive, complementary technique for the diagnosis of minimal conduction block in patients with normal findings in standard nerve conduction studies.