## INTRODUCTION

Peripheral neuropathy (pn) encompasses a large spectrum of peripheral nervous system disorders with a wide range of causative factors. The overall prevalence of PN is challenging to determine given the diverse etiologies. Diabetic PN is the most common cause of neuropathy with prevalence rates in type 1 diabetics of up to 34%, and up to 25% in type 2 diabetics.1 Those with asymptomatic but electrodiagnostically present disease increase the rate to as high as 54%.2 PN is particularly common in the elderly, with a prevalence in older Americans being as high as 20%; 10% of this population is individuals aged 60 years with diabetic PN, with another 10% being attributed to other causes.3

It is important to recognize PN and intervene in a timely fashion to manage the primary disease when possible, as well as prevent and manage serious complications. PN can have significant effect on function and day-to-day quality of life, particularly in older adults. It may also be the presenting manifestation of underlying disease or indicate environmental or iatrogenic toxicity requiring prompt identification and elimination of the causative agent.

## CAUSES OF PERIPHERAL NEUROPATHY

PN can be classified first by the type and distribution of nerve fibers affected and its structures involved, and second by the underlying causative agent.

PN is further characterized along three axes. The first is the type of nerve fiber affected: sensory, motor, or small fiber. The second axis is the degree to which the PN affects the nerve axon itself or the myelin sheath. And the last consideration is the distribution of nerves affected, in either a diffuse pattern, usually with a distal-to-proximal gradient, or if it presents with an asymmetrical or patchy distribution. The patient's history and physical examination often point to where on these axes their neuropathy falls, with electrodiagnostic studies further refining these findings. These patterns of nerve involvement aid in pointing toward the underlying causative disease or agent (Table 11–1).

Table 11–1Common Etiologies of PN by Pattern of Nerve Structures Affected

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