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.
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.
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
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.
The ventral, or anterior ...