Kartierung von Nervpathologien mittels Mehrkanalelektroneurographie
Clinical electroneurography, the diagnostic standard for the assessment of thickly myelinated peripheral nerves, is of limited spatial resolution since it provides only average data (nerve conduction velocity, nerve or muscle action potential amplitude) on relatively large nerve segments. Accordingly, different distribution patterns of pathologies cannot be distinguished: axon pathologies result in the same net amplitude decrease, myelin pathologies in the same conduction velocity reduction irrespective of the location and extent of the destruction. But precisely the distribution and type of nerve damage is relevant to ensure correct diagnosis and therapy. These range from spontaneous recovery to highly sophisticated chronic treatment regimens, which are often expensive - both financially and in terms of burden for the patient. Hence, our main objective is to optimize the diagnostic specificity by developing a finer grained functional-spatial model consisting of a multichannel neurographical approach combined with ultrasound data. Based on ultrasound, eight electrodes are positioned along the course of the median and ulnar nerves and nerve depth (distance to skin) profiles are recorded. Bipolar direct current stimulation is applied in the palm of the hand, resulting in the excitation of both motor and sensory nerve fibers (mixed nerve technique) such that eight mixed nerve action potentials (MNAPs) can be recorded along the nerve. We performed measurements in ten healthy volunteers and twelve times in patients (4 CIDP, 2 MMN, 5 GBS, 1 CTS). We found a constant nerve conduction velocity over all segments in healthy subjects. Also, we determined a relevant amplitude decay as a function of the distance to the surface recording-electrode (inverse-square law) and an amplitude decay as a function of the distance to the stimulation electrode (temporal dispersion). We present the attempt of an amplitude signal adjusted to depth from the surface. Furthermore, we assess disease specific characteristics such as focal demyelination in CIDP patients. Using the setup described, we reliably obtain MNAP and their latencies of two peripheral nerves along their course without averaging. Unfortunately, the measurement of diseased nerves with reduced MNAPs is more difficult owing to limited sensitivity. In the future, measurements with needle electrodes might contribute to a better understanding of peripheral nerve pathologies.
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