Can Low-Level Laser Therapy Have An Impact For Small Fiber Neuropathy?

Kerry Zang, DPM, Janna Kroleski, DPM, Shahram Askari, DPM, and Sanford Kaner, DPM

In addition to reviewing diagnostic testing for small fiber neuropathy and current treatments, these authors discuss recent study results for low-level laser therapy.

Diabetic neuropathy is the most common diabetes-related comorbidity. Diabetic neuropathy impacts between 60 to 70 percent of all patients with diabetes. The burden to treat this disorder will only intensify as current trends predict that more than 360 million individuals worldwide will be diagnosed with diabetes by the year 2030.1,2

   Neuropathy can have serious detrimental effects on a patient’s quality of life. Patients with diabetic neuropathy have a 1.7-fold greater risk of amputation and a 25 to 50 percent higher mortality rate in comparison to those diabetic patients without neuropathy.3 Neuropathy of the lower extremity is tightly coupled with the development of pain or discomfort, restricted activity, and foot ulcers.

   One would determine the classification of neuropathy by the fiber type that is directly affected. Small fiber neuropathy (SFN) is one prevalent form of neuropathy that affects small fiber sensory neurons.4 Small fiber neuropathy results from nerve ischemia, direct effects of hyperglycemia on neurons and intracellular metabolic modulations that impair nerve function.5 Small fiber neurons are cytoplasmic extensions of the dorsal root ganglion neurons that innervate skin and visceral organs, and are responsible for the transmission of thermonociceptive stimuli. Small fibers include myelinated A-δ fibers and unmyelinated C fibers. Somatic fibers innervate the skin and voluntary muscles whereas autonomic fibers innervate cardiac and smooth muscles.6 Ischemia-induced small-fiber nerve degeneration results in clinical symptoms including pain or discomfort, numbness, and loss of temperature sensation.4,5,7 In addition to vascular deficiencies, researchers have reported perivascular inflammation involving macrophages and T cells, and believe this promotes further nerve degeneration.8

Keys To The Clinical Presentation Of Small Fiber Neuropathy

The clinical manifestation of neuropathic pain is derived from the degeneration of large diameter or small diameter sensory nerves. Large fiber sensory nerves or large fibers are responsible for the transmission of proprioception and vibration sensation.9 Large fiber disruption commonly leads to paresthesias, muscle weakness, impaired balance and absent or reduced tendon reflexes.4 Clinical examination using electrodiagnostics, including electromyography (EMG) and nerve conduction velocity studies, help classify the type of neuropathy. Physicians may use EMG to evaluate the extent of axon degeneration by assessing sensory action potential amplitudes and intervention.7 Demyelinating neuropathy consistently presents with decreased nerve conduction velocity, prolonged terminal latency, temporal dispersion and blocked conduction.9

   The clinical presentation of individuals with small fiber neuropathy includes pain, paresthesias, loss of two-point discrimination, loss of thermal perception, xerosis and sometimes diminished Achilles deep tendon reflex and loss of the superficial reflexes.10 The diagnosis of small fiber neuropathy with traditional methods including nerve conduction studies is difficult as small fibers are undetectable. Therefore, the diagnosis of small fiber neuropathy often occurs as a result of positive sensory symptoms.11

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