Laboratory Studies
The following laboratory studies are indicated:
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Chemistry profile - Chronic alcohol consumption may cause an increase in liver enzyme levels (eg, aspartate aminotransferase, alanine aminotransferase, gamma glutamyltransferase).
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Diabetes testing - Peripheral neuropathy may be among the first presenting symptoms associated with diabetes mellitus (DM); however, the majority of electromyographically diagnosed diabetic peripheral polyneuropathies occur in patients with long-standing histories of diabetes mellitus. Hemoglobin A1C can be used to estimate average blood glucose levels over the course of previous months.
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Creatinine level - Renal insufficiency indicated by elevated blood creatinine levels also may be a cause for peripheral neuropathy.
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Thiamine, vitamin B-12, and folic acid levels - These essential vitamins play an important role in the proper functioning of the peripheral and central nervous systems and should be the among the first laboratory tests ordered on a patient with polyneuropathy. Nutritional deficiencies associated with alcoholism are common and may contribute to the development of neuropathy in alcoholic patients (see Pathophysiology). [5]
The following laboratory tests are ordered once more common diagnoses are essentially excluded:
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Screen for heavy metal toxicity. The toxicity of lead and other heavy metals is a well-known cause of neuropathy.
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Determine the erythrocyte sedimentation rate. It may be elevated in patients with symptoms of a peripheral polyneuropathy, owing to an inflammatory condition (eg, paraneoplastic syndrome).
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Test for human immunodeficiency virus (HIV) infection and venereal disease. Distal symmetric polyneuropathy is a common complication of HIV disease and can be an early manifestation of HIV infection. [26] Recent research suggests that HIV-infected patients who use illicit substances such as alcohol are at a higher risk for developing distal symmetric polyneuropathy. [27] Syphilis should also be considered as a cause of neuropathy.
Imaging Studies
Radiographic evidence of distal neuropathic arthropathy may also be present as a result of long-term sensory deficits.
Other Tests
Nerve conduction studies (NCSs)
Although not specific for alcoholic neuropathy, NCSs can help to clarify the diagnosis and can to some extent quantify the amount of peripheral neuropathy present, when comparisons are made with age-adjusted normal values. However, nerve conduction velocities (NCVs) are generally normal or mildly slowed in patients with alcoholic neuropathy. Some fast-conducting axons can be spared, preserving measured velocity until axon loss has severely progressed. Demyelinating neuropathies show a greater loss of conduction velocity. Note the following:
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Sural/superficial peroneal SNAP - In ethanol (ETOH) neuropathy, the response may be absent or the amplitude may be significantly reduced. The superficial peroneal SNAP generally is more difficult to obtain than is the sural in average patients, including elderly individuals; therefore, it is less specific for pathology. The sural SNAP should be readily obtainable in most patients, including those of advanced age.
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Tibial/peroneal compound motor action potential (CMAP) and NCV to intrinsic foot muscle - In ETOH neuropathy, test results may show significantly reduced amplitude. Results may demonstrate slowing of NCV below the reference range.
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Ulnar/median SNAP - Consider performing this test to evaluate the extent of neuropathy if lower extremity sensory studies suggest abnormalities.
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Ulnar/median CMAP - Consider performing this test to evaluate the extent of neuropathy if lower extremity motor studies suggest abnormalities.
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Tibial H-reflex - In ETOH neuropathy, the patient may have an absent response or may have symmetrically reduced amplitude or increased latency. Typically, this is thought to be the most sensitive of electrophysiologic tests, with some studies quoting rates as high as 50%.
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T-wave - One study found that the T-wave is somewhat more sensitive for alcoholic neuropathy. [28]
Needle electromyography (EMG)
Needle EMG is based on presentation. A typical peripheral neuropathy screen will involve a proximal muscle and a distal one in the lower and upper extremities.
A more extensive screen also may be useful in evaluating for the presence of a concomitant lumbosacral radiculopathy.
Significant abnormalities seen in patients with ETOH neuropathy include the presence of positive sharp waves and/or fibrillation potentials. Complex, repetitive discharges also may be observed. However, if the NCSs are normal, the presence of positive sharp waves in 1 intrinsic foot muscle is not necessarily indicative of neuropathic pathology. Occasionally, intrinsic foot muscles display abnormal electromyographic potentials in asymptomatic people.
If lower extremity muscle abnormalities are detected, a sampling of upper extremity muscles is indicated to estimate extent of disease.
Vibrometer testing
Results may be useful in detecting early signs of subclinical neuropathic disease.
