2 - CONDUCTION IN ABNORMAL NERVE

Abstract

This chapter describes the basic and clinical physiological consequences of the main patterns of injury and repair affecting the peripheral nervous system. To the clinical electrophysiologist, the basic pathological changes in peripheral nerves that are most amenable to testing and measurement are those that alter conduction velocities and reduce the numbers of axons. These changes can be the result of either block in the transmission of their impulses or degeneration and actual loss of the axons. To emphasize these basic priorities, the patterns of injury and repair in the peripheral nervous system have been divided. Demyelination may be primary or secondary to neuronal or axonal degeneration. In primary demyelination, the main injury is to the Schwann cell or myelin. Degenerative changes in axons may be present in these neuropathies, but they are in general much less prominent. Secondary demyelination is common in degenerative neuronal and axonal disease. It is a common accompaniment of axons undergoing degeneration and is most complete and extensive toward the extremities of the degenerating axons. In both the primary and secondary varieties, myelin retraction and breakdown occur near the nodal regions, producing paranodal demyelination. Later the demyelination becomes more extensive and may come to occupy the whole internode segment to produce so-called segmental demyelination.