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In this single chapter, an attempt is made to provide an overview of the very large and difficult subject of peripheral nerve disease. Because the structure and function of the peripheral nervous system are relatively simple, one might suppose that our knowledge of its diseases would be fairly complete. Such is not the case. For example, when a group of patients with chronic polyneuropathy were investigated intensively in a highly specialized center for the study of peripheral nerve diseases several decades ago, a suitable explanation for their condition could not be found in 24 percent (Dyck et al, 1981) and even more discouraging figures prevail in our clinics today. Moreover, the physiologic basis of many neuropathic symptoms continues to be elusive and in several of the neuropathies the pathologic changes have not been fully determined.

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There has, however, been a surge of interest in diseases of the peripheral nervous system, which promises to change this state of affairs. Electron-microscopic studies, quantitative histometric methods, and refined physiologic techniques have expanded our knowledge of the structure and function of peripheral nerves over the past 25 years and rapidly advancing techniques in the fields of immunology and molecular genetics are now clarifying entire categories of neuropathic disease. Also, in recent years, effective forms of treatment for several peripheral neuropathies have been introduced, making accurate diagnosis imperative. For these reasons, clinicians now find the peripheral neuropathies among the most challenging and gratifying categories of neurologic disease.

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It is important to have a clear concept of the extent of the peripheral nervous system (PNS) and the mechanisms by which it is affected by disease. The PNS includes all neural structures lying outside the pial membrane of the spinal cord and brainstem with the exception of the optic nerves and olfactory bulbs, which are but special extensions of the brain. The nerves within the spinal canal and attached to the ventral and dorsal surfaces of the cord are called the spinal roots; those attached to the ventrolateral surface of the brainstem are the cranial nerve roots, or cranial nerves.

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The dorsal, or posterior (afferent, or sensory), spinal roots consist of central axonal processes of the sensory and cranial ganglia. On reaching the spinal cord and brainstem, they extend for variable distances into the dorsal horns and posterior columns of the cord and into the spinal trigeminal and other tracts in the medulla and pons before synapsing with secondary sensory neurons, as described in Chap. 9. The peripheral axons of the dorsal root ganglion cells are the sensory nerve fibers. They terminate as freely branching or specialized corpuscular endings—i.e., the sensory receptors—in the skin, joints, and other tissues. The sensory nerve fibers vary greatly in size and in the thickness of their myelin covering; based on these dimensions, they are classified as type A, B, or C, as discussed in Chap. 8.

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The ventral, or anterior ...

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