New developments in electromyography and in peripheral conduction studies

Modern electrophysiological diagnostics is characterised by the increasing use of computers in recording procedures and in the interpretation of findi ngs. Two technical approaches are available in electromyography (EMG): anal ysis of the interference pattern and of the automatic motor unit action pot ential (MUAP). Computer-aided diagnosis has the advantage of being time - s aving as compared to traditional manuel techniques and is more independent of the experience and skill of the examiner. Its use is, however, restricte d by the problem of building up adequate reference values and estimating th e optimal relation between sensitivity and specificity for the different va riants of each method. In contrast to these quantitative analysis methods, the "unblanketing techn ique" in traditional EMG demonstrates the dynamic features of motor units. This technique focuses on the principle part of the MUAP by removing low-fr equent contributions by remote fibres and allows to estimate an increased f ibre density and conduction instabilities in immature collateral sprouting. Measurement of the muscle fibre conduction velocity or recordings of the mu scle or motor unit twitch force yield additional information on muscular fu nction, but those techiques are probably still too sophisticated for clinic al routine use. Computer-aided analysis in conduction studies allows to measure for example the area of the total or the negative peak of an MUAP in addition to the p eak-to-peak amplitude. The value of these parameters to describe conduction abnormalities due to slight demyelination or axon loss is discussed. It ca n be concluded that area measurements seem to be more appropriate for detec ting a conduction block. Finally we give an overview of the current state in the diagnosis of carpal tunnel syndrome (CTS). Comparative sensory conduction studies of median an d ulnar nerves as well as the sensory conduction ratio between finger-wrist and palm-wrist are most sensitive in detecting mild CTS. The median-ulnar motor latency difference to the 2nd interosseus dorsalis and 2nd lumbrical muscle is the most appropriate technique to discriminate between severe CTS and polyneuropathy.