Peripheral neuropathy: clinical and electrophysiological considerations

Abstract

This article is a primer on the pathophysiology and clinical evaluation of peripheral neuropathy for the radiologist. Magnetic resonance neurography has utility in the diagnosis of many focal peripheral nerve lesions. When combined with history, examination, electrophysiology, and laboratory data, future advancements in high-field magnetic resonance neurography may play an increasingly important role in the evaluation of patients with peripheral neuropathy.

Keywords: Electromyography; Entrapment neuropathy; Hereditary neuropathy; Nerve conduction study; Neuroimaging; Peripheral neuropathy.

Figure 1

Plastic sections of sural nerves stained with Toluidine Blue at 10X (A-C) and 100X (A’-C’). (A) Normal nerve showing normal density of myelinated nerve fibers. “endo” is endoneurium, “peri” (arrow) is perineurium surrounding fascicles, “epi” is epineurium. At high magnification (A’), large, thickly myelinated fibers (*) can be distinguished from smaller, thinly myelinated fibers (arrow). (B) Sural nerve from a patient with axonal neuropathy showing a fascicle with markedly reduced nerve fiber density. (B’) shows a fiber with a “myelin ovoid”, which can be seen in Wallerian degeneration. (C) Sural nerve from a patient with Charcot-Marie-Tooth Disease type 1A. The nerve is diffusely enlarged (C), and at high magnification (C’), shows nerve fibers undergoing cycles of demyelination and remyelination, resulting in the typical “onionbulb” appearance (*).

Figure 2

Median and ulnar motor nerve conduction study showing partial motor conduction block in the forearm segment in a patient with acquired demyelinating polyneuropathy. Note that with stimulation above the elbow, the amplitiude (vertical blue lines) of the motor response is diminished (due to conduction block) when compared with the response at the wrist. Also, the duration of the response (horizontal red lines) is prolonged with stimulation above the elbow due to temporal dispersion, a common feature of demyelination.

Figure 3

Vasculitic neuropathy: the plastic section with toluidine blue staining shows a striking fascicle-to-fascicle variation of fiber density in the two adjacent fascicles. Mild subperineurial edema can also be appreciated in this section.

Figure 4

Congo Red stain shows apple green birefringence under polarizing microscope. Note that the amorphous birefringent material invades into the vessel wall.