Electrodiagnostic Evaluation of Peripheral Neuropathy

Peripheral neuropathy, also known as peripheral polyneuropathy, is a general term for a broad range of disorders that cause damage and dysfunction of the nerves of the peripheral nervous system in several different patterns. Electrodiagnostic (EDX) testing can not only identify whether or not peripheral neuropathy may be present. Still, it can also help give the clinician information to determine the disorder's etiology, severity, and prognosis. Thorough history taking, physical examination, and EDX are all integral to the evaluation and treatment of patients presenting with symptoms of peripheral neuropathy. Although peripheral polyneuropathies are commonly found in patients with diabetes mellitus or excessive alcohol use, many medical conditions have associations with peripheral neuropathies. Peripheral polyneuropathies can be acquired, such as in diabetes mellitus, amyloidosis, HIV, or cis-platinum chemotherapy, while some may be inherited, as in Charcot-Marie-Tooth.  Common symptoms of most peripheral polyneuropathies involve paresthesias, numbness, or pain in the distal extremities, such as in the feet or hands. Some can present acutely, while many have a more insidious onset. A patient may describe difficulty with buttoning their clothes or tripping over their feet, which may be signs of worsening weakness and progression of the disease. Inherited polyneuropathies may present with ataxia and muscle cramping, while acquired polyneuropathies typically present as burning or paraesthesias.  EDX can be useful in finding an etiology and thus guiding treatment. Therefore, obtaining a detailed history, including medications, diet, social/occupational history, and family history is critical. Exposure to heavy metal toxins or certain medications, such as vincristine and amiodarone, or a medical history significant for hypothyroidism or vitamin b12 deficiency indicate a risk for developing peripheral polyneuropathies. Patients with a family history of hereditary motor and sensory neuropathies (HMSN) such as Charcot-Marie-Tooth Type 1 disease (HMSN I) or Refsum’s disease (HMSN IV) might point the clinician toward a hereditary cause for the neuropathy. Infectious diseases such as Lyme disease and HIV and autoimmune-mediated diseases such as acute inflammatory demyelinating polyneuropathy or chronic inflammatory demyelinating polyneuropathy can also present with symptoms of peripheral neuropathy.  The physical examination may also assist in identifying the etiology and characteristics of peripheral neuropathy. Patients with diabetic peripheral neuropathy often describe a “stocking-glove” distribution of numbness in the hands and feet. Deafness, cataracts, or musculoskeletal deformities point toward a hereditary cause. A predominant sensory neuropathy may have decreased light touch or vibration sensation, while distal muscle weakness and decreased deep tendon reflexes may indicate a motor-predominant neuropathy. For example, a patient on dapsone therapy may present with weakness and abnormal deep tendon reflexes and has electrodiagnostic findings of primarily axonal motor neuropathy. A patient who had high dose cis-platinum therapy may have preserved deep tendon reflexes and muscle strength but complained of abnormal sensation, as well as other drug side effects such as ototoxicity and gastrointestinal upset. In cis-platinum peripheral neuropathy, EDX often yields the presence of a primarily axonal sensory neuropathy.