Diagnostic tools that may aid in diagnosis of neuropathic pain
Electrodiagnostic studies like electromyogram (EMG) and nerve conduction studies can sometimes be helpful in confirming existence of a neurologic lesion. Some patients may dislike these tests, as they require many tiny needle electrodes to be placed, often in painful areas. Thermography, quantitative sensory testing (QST), and quantitative sudomotor axon reflex testing (QSART) may be useful in confirming autonomic dysregulation. Skin biopsy is used to assess intraepidermal nerve fiber density (IENFD) and determine severity of axon loss in patients with possible small-fiber sensory neuropathy. Functional magnetic resonance imaging (fMRI) has been useful in research regarding central pain mechanisms, but it is unclear what, if any, role this modality may have in diagnosis or routine clinical care.
Are any labs useful?
Judicious laboratory testing will be dependent on suspected etiology and risk factors. Labs to consider if a disease state is suspected include complete blood count, comprehensive metabolic panel, liver function tests, fasting blood glucose, hemoglobin A1C, thyroid stimulating hormone, and serum vitamin B12 level. Vitamin D level (deficiency is associated with painful peripheral neuropathy) and erythrocyte sedimentation rate (elevated in various autoimmune, infectious, and other system conditions) may also be useful. If a specific cause of neuropathy remains elusive, more extensive testing based upon the history and physical examination such as HIV, Lyme antibody, rapid plasma reagin (RPR), antinuclear antibody, or paraneoplastic syndrome testing should be considered.