[Diagnostic criteria of conduction block and the spectrum of diseases which is accompanied with conduction block].

To establish the criteria of conduction block is essential for its clinical application. Nerve conduction studies were performed on 15 normal controls. Peak-to-peak amplitude, negative wave area and negative wave duration were measured and their ratios between proximal and distal stimulation were estimated. The results were summarized in Table. Decrease of amplitude and area was the more conspicuous in the longer segment, and therefore it was suspected to be due to the duration-dependent phase cancellation. Since area reduction was less than the amplitude reduction, the area was a more useful parameter than the amplitude. The importance to provide different normal values for the different nerve segment was emphasized. The diseases which are known to be accompanied with conduction block include AIDP, CIDP and entrapment neuropathy. Multifocal motor neuropathy with conduction block associated with anti-GM1 antibody is recently noticed and we presented the cases we experienced. By contrast, it has been demonstrated that HMSN type 1 does not show conduction block. We examined diabetic and uremic neuropathies and showed that they do not have conduction block. These facts suggest that the demyelination does not always produce conduction block.