Can Low-Level Laser Therapy Have An Impact For Small Fiber Neuropathy?
Depending on the history and physical examination, the following laboratory studies may be indicated: complete blood count, comprehensive metabolic panel, lipid panel, blood urea nitrogen, creatinine, electrolytes, thyroid stimulating hormone, free thyroxine (T4), antinuclear antibody, extractable nuclear antigens, angiotensin-converting enzyme, serum and urine immunofixation tests, hemoglobin A1c, serum B-1, B-6, B-12, and folate levels, vitamin E, and erythrocyte sedimentation rate. If you have a strong index of suspicion, you can pursue heavy metal testing as well.
One would only utilize EMG and nerve conduction velocity studies to ascertain the presence of large fiber neuropathy because of the inability to measure the action potentials of small fibers. Electromyography is a test that measures the response of muscle to nerve stimulation. Since small fiber nerves generally do not innervate neuromuscular junctions, this test is usually normal with small fiber involvement unless there is combined small and large fiber neuropathy.6
Neurodiagnostic pathology techniques are emerging as the gold standard for the diagnosis of small fiber neuropathy. Intraepidermal nerve fiber density is consistently reduced in individuals with neuropathy.25,26 Immunohistochemical use of an antibody against protein gene product 9.5 yields a high quality analysis of unmediated epidermal nerve endings.6
Physicians have used this approach to identify reduced nerve fiber density in both the dermis and epidermis in patients with neuropathy. It allows one to quantify and compare nerve fiber loss and degeneration to an established normal range for the lower leg and the foot. One can repeat this procedure at appropriate intervals to monitor small fiber nerve loss.
Serial biopsies are advantageous for staging the severity of neuropathy and determining the effectiveness of any neuromodulation therapy. One can obtain biopsies from the dorsum of the foot and the distal third of the lateral aspect of the lower leg. Physicians can obtain a skin punch biopsy with aseptic techniques by utilizing a local anesthetic and a 3 mm punch biopsy instrument.
Current And Emerging Treatments For Small Fiber Neuropathy
Once you make the diagnosis of small fiber neuropathy, there are several treatment options to consider. Historically, physicians have directed treatment toward controlling pain. Pharmacological treatment has included the use of antidepressants, anticonvulsants, sodium channel blockers and opioid analgesics. Various studies have shown that these modalities have some effect in controlling neuropathic pain, but they have side effects that one must monitor.
In addition, clinicians have used local anesthetic patches, local anti-inflammatory neuromodulation agents in transdermal gels, physical therapy, acupuncture and various forms of relaxation techniques including biofeedback.
More recently, physicians have utilized a nutraceutical approach with promising results. Metanx (Pamlab, LLC) is a prescription nutraceutical, which contains bioavailable forms of L-methylfolate (2.8 mg), pyridoxal 5'-phosphate (25 mg) and methylcobalamin (2 mg) that have been shown to have a positive response in small fiber neuropathy.27 Early preliminary studies have shown regrowth of small nerve fibers after several months of treatment. There are very few adverse effects when utilizing the nutraceutical approach.
Overall though, therapeutic options for SFN are limited with most therapies attempting to address the underlying immune-mediated aspects. The use of simple analgesics, anticonvulsants or antidepressants does not address the important etiologies of SFN, which include ischemia and nerve degeneration. An effective therapeutic approach would promote angiogenesis, downregulate inflammation and induce small fiber nerve regeneration.