Diagnostic Testing for Neuropathy

Numerous diagnostic tests are available for evaluation of neuropathies. The main aim of these diagnostic tests is to assess the degree of nerve damage and ascertain its cause. Various types of diagnostic tests are used in evaluation of neuropathies and the most notable being the electrodiagnostic studies, nerve biopsies and various lab tests.

Nerve Conduction Studies and Needle Electromyography together comprise the electrodiagnostic studies. These studies often provide important diagnostic clues to the specific cause of neuropathy. Nerve conduction studies can differentiate between neuropathy due to degeneration of nerve axons and the neuropathy due to segmental demyelination. Nerve conduction studies also elucidate exact extent and degree of involvement of various nerves and whether any specific subsets of nerves are involved or not. In Needle Electromyography, the electrical activities of voluntary muscles are recorded and studied for any abnormality. Unlike nerve conduction studies, the electromyography studies may be also abnormal in diseases of muscles.

Numerous methods are used to assess the involvement of the autonomic nervous system. Such studies include recording of changes in heart rate with deep breathing, changes in heart rate and blood pressure when performing Valsalva maneuver (attempting to exhale air out of the lungs while keeping the airways closed), changes in blood pressure when standing up from a lying down position and many others. Sometimes, the NCS may be normal while subtle hints to the diagnosis might be provided by these studies.

Various laboratory tests can also provide important clues to the cause of neuropathy. Patients with neuropathy are always evaluated for diabetes mellitus. The lab tests done for diabetes are Fasting Blood Glucose and Glycated Hemoglobin levels in the blood, and an Oral Glucose Tolerance Test if these two are normal. A 'heavy-metal screen' is also available and is done when there are clinical findings or history suggestive of possible exposure to heavy metals like lead, arsenic, thallium etc. In certain diseases, Guillain-Barre Syndrome, for example, lumbar puncture is done and the cerebrospinal fluid so obtained is analyzed for abnormalities. Other than these, routine evaluation with complete blood count, basic chemistries (including serum electrolytes), urinalysis, Erythrocyte Sedimentation Rate, Rheumatoid Factor, Antinuclear Antibodies and tests to assess the function of kidney, thyroid and liver are also done. Levels of Vitamin B12 and Folate are measured to check if neuropathy is due to deficiency of these.

Various auto-antibody panels are available for quick screening in neuropathy patients, but they have no proven additional advantage over complete clinical examination and electrodiagnostic studies.

Nerve Biopsies are rarely needed and are only used when nerve conduction studies are abnormal. Nowadays, the nerve biopsies are done when there is suspicion of certain specific disease like amyloid neuropathy or vasculitis. The nerve most commonly used is sural nerve (present in lower limb). Very rarely, sometimes skin biopsy is also done if small-fiber neuropathy is suspected.