Peripheral Neuropathy: Clinical and Electrophysiological Considerations

Key points

Basic structure of peripheral nervous system

The peripheral nervous system refers to the part of the nervous system outside of the brain and spinal cord. Functionally, peripheral nerves are categorized into motor, sensory, and autonomic nerves. The cell bodies (soma) of motor neurons reside in the ventral gray matter of the spinal cord and are called anterior horn cells. Motor fibers often have very long axons that extend all the way to the neuromuscular junction. A motor unit consists of an anterior horn cell, its motor axon, and all the

Pathophysiology of peripheral nerve injury

Regardless of its cause and nature of injury, peripheral nerve reaction to injury is limited to certain types of physiologic changes, depending on the extent of injury (Table 1). Minor, local insult to a peripheral nerve will result in a transient, focal conduction block, whereas intermediate insult may cause focal demyelination that requires a longer period of time for recovery. If the extent of nerve injury is severe enough to disrupt its axonal contents, a series of physiologic changes known

Clinical assessment of peripheral nerve injury

When evaluating patients with neuropathy or nerve injury, it is very important to assess the physiologic status of peripheral nerves with nerve conduction studies to correlate their physiology with their clinical symptoms. Once the physiologic status of the nerve injury is assessed, its temporal progression, severity, and anatomic distribution should be carefully determined to reach an accurate diagnosis.

Entrapment mononeuropathies

Carpal tunnel syndrome is the most common mononeuropathy and is caused by entrapment of the median nerve as it runs in the carpal tunnel at the wrist. Other common entrapment neuropathies include ulnar neuropathy at the elbow (cubital tunnel syndrome), radial neuropathy at the spiral groove, and peroneal neuropathy at the fibular head. Conditions that predispose to carpal tunnel and cubital tunnel syndrome include occupations that undergo repetitive flexion/contraction of the wrists and elbows,

Neuropathies Associated with Metabolic Disease

Neuropathies associated with metabolic disease typically present with a slowly progressive, distal (length-dependent) symmetric sensorimotor polyneuropathy (DSPN) with physiologic features of axonal loss.

Inflammatory and immune-mediated neuropathy

The immune-mediated neuropathies are a heterogeneous group of disorders wherein the immunologic process may be directed to either peripheral nerves or the supporting blood vessels. Peripheral nerve myelin is the usual target in demyelinating neuropathy. In vasculitic neuropathy, the pathologic process originates in the blood vessels and leads to nerve ischemia, resulting in a neuropathy characterized by multifocal sensory and motor axonal loss.

Vasculitic neuropathy

Vasculitic neuropathy is an immune-mediated disorder directed against blood vessels, resulting in ischemia and infarction to the peripheral nervous system.²⁶ Vasculitic involvement of the peripheral nerves typically causes multiple, focal areas of ischemic injury. The clinical presentation is typically initially one of multiple mononeuropathies (also called mononeuritis multiplex), but over time, may develop into a distal symmetric polyneuropathy. Patients typically present with an acute onset

Hereditary neuropathy

Also known as Charcot-Marie-Tooth disease, the hereditary motor and sensory neuropathies encompass the largest group of inherited neuropathies. These diseases are commonly classified based on clinical presentation (age of onset and inheritance pattern) and pathologic abnormality/electrophysiology (axonal: CMT2 vs demyelinating: CMT1).27, 28

Neuropathies associated with amyloid protein

Amyloids are insoluble aggregates of various proteins that share common 3-dimensional structure of β-pleated sheets and are resistant to proteolytic decomposition. Amyloidosis refers to a variety of conditions whereby amyloid protein accumulates in any organ, including peripheral nerves, leading to dysfunction. Amyloid deposits have characteristic apple-green birefringence when stained with Congo red and seen under a polarizing microscope and may be detected on nerve biopsy (Fig. 4).

Toxic neuropathy

From a practical perspective, it is often difficult to prove causality when a toxic neuropathy is suspected.³⁰ However, finding the cause should not be neglected, as toxic neuropathy is one of those conditions whereby treatments are available, if diagnosed timely. Although many clinicians regard toxic neuropathy as a diagnosis of exclusion, it was found to be very helpful to use quantitative measurement tools, such as the TNS to appreciate the temporal relation of disease’s severity and a

Summary

Peripheral nerves are affected by a broad spectrum of disorders. With technical advances that permit high-resolution MR, peripheral neuroimaging is gaining utility in evaluation of peripheral nerve disorders. MR neurography is especially useful in evaluating proximal nerve lesions that are not easily assessable with nerve conduction study; for example, MR neurography will not only provide better diagnosis of a tumor compressing the brachial plexus than an electrophysiological study but also aid