Several types of neuropathies are particularly prone to recurrence: CIDP, Refsum disease, Tangier disease, and porphyria, the last of which may display attacks that recur spontaneously or are precipitated by the administration of various drugs. Repeated exposure to environmental toxins can do the same. Approximately 2 percent of patients with GBS have one or more relapses, in which the clinical and pathologic changes differ little between episodes. Some instances of mononeuritis multiplex, especially when associated with cryoglobulinemia, are also characterized by remissions and relapses over many years, although the remissions are incomplete. A common cause of relapse is the withdrawal of corticosteroids in CIDP patients who are dependent on these drugs; similarly, lapses in the treatment of paraproteinemic neuropathies cause similar fluctuations in symptoms. Enlargement of nerves may occur with repeated attacks from any of these diseases. It is self-evident that patients who have recovered from an episode of alcoholic–nutritional or toxic polyneuropathy will develop a recurrence if they again subject themselves to intoxication or nutritional deficiency.
Neuropathic symptoms that fluctuate in relation to environmental factors such as cold (cryoglobulinemia), heat (Fabry and Tangier diseases), or intermittent exposure to heavy metal or other type of poisoning may simulate an inherently relapsing polyneuropathy.
The diagnosis of this group of neuropathies rests on the finding of motor, reflex, and sensory changes confined to the territory of a single nerve; of several individual nerves affected in a random manner (mononeuritis or mononeuropathy multiplex); or of a plexus of nerves or part of a plexus (plexopathy). Certain neuropathies of this type—traceable mainly to polyarteritis nodosa or other vasculitides, leprosy, sarcoid, or diabetes—have already been discussed and are the main causes of the multiple mononeuropathy pattern. In addition to the signs of mononeuropathy multiplex, pain overlying the site of nerve infarction or distally is characteristic. The CSF protein is usually normal or slightly elevated, and in certain of these diseases there is a CSF pleocytosis (e.g., HIV, Lyme disease). Inflammatory neuropathy and the multifocal motor neuropathy caused by antibodies to GM1 also may be considered, because of their clinical similarity, in this group.
In identifying a process as caused by single or multiple mononeuropathies, the reader can refer to Table 43-1, which lists the roots, nerves, and muscles that are involved in particular movements, and to Table 43-4, which gives the main etiologies of mononeuropathy multiplex.
Brachial plexus neuropathies, or brachial plexopathies, comprise an interesting group of neurologic disorders. Most develop without apparent cause and manifest themselves by sensorimotor derangements ascribable to one or more of the cords of the plexus. Some are a result of infiltration by tumor, compression, obscure infections (possibly viral), and the delayed effects of radiotherapy. Of obvious cause are those that result from trauma, in which the arm is hyperabducted or the shoulder violently separated from the neck. Difficult births are an important source of such traction injuries to the plexus, but their nature is also evident. Rarely, the brachial plexus or other peripheral nerves may be damaged at the time of an electrical injury, either from lightning or from a household or industrial source (see “Electrical Injuries” in Chap. 41).
Most common in this category is an idiopathic brachial plexus neuritis of obscure origin, also called Parsonage-Turner syndrome, discussed further on. It stands apart as a special clinical entity, often difficult to distinguish from other types of brachial and axillary pain. Some of these cases, surprisingly, are familial; others occur in small outbreaks, but most are sporadic.