Painful polyneuropathy (PN) is a debilitating neurologic problem and frequently a challenging therapeutic management issue. Difficulties in managing patients are too often the result of poor understanding of their problem on the part of the treating physician. Many physicians assume that there is no need to work up neuropathy because the final outcome is likely to be an idiopathic, axonal disorder for which there is no effective therapy. In fact, many neuropathies are responsive to immunosuppressive and other conservative therapies. Although responses to such therapy constitute the minority, they should be vigorously sought before telling patients there is no treatment for their progressive disorder. In many cases, treatment of the PN also leads to improved pain control; however, pain is often a primary issue in and of itself and must be treated irrespective of the potential for improvement of the underlying PN. In these cases, pain management specialists may work in concert with neurologists to provide a comprehensive treatment approach.
CLINICAL ISSUES IN POLYNEUROPATHY
The first step in developing a rational approach to patient management is obtaining a working knowledge of the underlying disorders that fall under the category of neuropathy. Although it is often used loosely to refer to PN, the term neuropathy is actually not specific and implies any peripheral nerve lesion, focal or diffuse. Classification schemes used widely among peripheral neurologists are based on anatomic and physiologic characteristics of the various disorders affecting peripheral nerves. The use of these classifications is not just an academic exercise but creates a basis for rational decision making in the evaluation and management of patients. The workup and treatment of individual patients with neuropathy must be approached with a basic understanding of the clinical behavior, including the anatomic and pathophysiologic characteristics, of the various neuropathic disorders.
CLASSIFICATION AND CLINICAL COURSE
The term polyneuropathy is used to describe a condition that is fairly symmetric and generalized, as opposed to focal neuropathy (mononeuropathy) or multifocal neuropathy (mononeuropathy multiplex [MM]). This chapter focuses on the diffuse disorders, including PN and multifocal mononeuropathies. These two groups of disorders may be indistinguishable clinically and are frequently accompanied by severe and disabling pain.
When a disorder of peripheral nerves is suspected, an attempt should be made to characterize the clinical features based on the time course, anatomic distribution, and physiology. Using this information, a reasonable differential diagnosis can be developed, which will determine appropriate further workup and management. This section further discusses the clinical and physiologic features of the diffuse neuropathies; their diagnostic evaluation is covered in the next section.
An important clue as to the etiology of a particular PN is its time course. Generally accepted guidelines classify a neuropathy ...