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

   Patients often complain that they have a feeling of a band around their foot or describe a sensation of wearing a tight sock even when barefoot. Pain can be constant or can occur at certain times, such as when they are in bed. Often, innocuous contact can become quite painful. This may include the wearing of shoes or irritation from sheets while in bed. However, positive sensory symptoms are not associated with only small fiber neuropathy as pain is also a common symptom of large fiber disorders.

   Patients with small fiber neuropathy may also present with negative symptoms including numbness, tightness and coldness.12 Generally, a patient’s symptoms are initially localized to the digits and plantar aspect of the foot but over time can spread proximally to the distal third of the leg. Often, the patient will start to complain of dysesthesia in his or her hands. This generally occurs after involvement of the lower leg.

   In addition to the involvement of small somatic nerve fibers, researchers have also reported involvement of small autonomic fibers.12 Autonomic symptoms can include modulation of sweating, skin discoloration, dry eyes and mouth, or facial flushing. Vascular dysregulation is a common occurrence with small fiber neuropathy and can manifest with localized edema and/or color and temperature changes in the lower extremities.13 Skin can become atrophic, thin and anhidrotic because innervating small fibers influence keratinocyte proliferation and thickness of the epidermis.14-17 Widespread autonomic involvement can have generalized distribution involving the gastrointestinal system, erectile dysfunction and cardiovascular and peripheral vascular involvement.12,18 Furthermore, small fiber neuropathy is associated with the onset of retinopathy. The diverse clinical presentation of small fiber neuropathy requires an interdisciplinary approach to effectively treat this disorder.

   All patients should have a detailed history and physical examination. This is especially true for patients with small fiber neuropathy. Questions regarding onset, progression, distribution and characteristics of symptoms all provide clues to the etiology. One should review the patient’s medical history and question him or her on family history, medications and possible toxic exposures. A comprehensive lower extremity evaluation should include vascular, neurologic, musculoskeletal and dermatologic examinations. However, even with the most comprehensive evaluation, the results are sometimes normal. Therefore, an effective therapeutic strategy may not be apparent when the underlying etiologies are undeterminable.

Pertinent Insights On The Diagnostic Workup

In the majority of cases, small fiber neuropathy is commonly linked to an underlying disorder that may include diabetes mellitus, impaired glucose tolerance, vasculitis, Sjogren’s syndrome, systemic lupus erythematous and numerous other conditions. However, the exact pathogenesis of small fiber neuropathy remains elusive. There is evidence for immune-mediated pathology in which pro-inflammatory cytokines such tumor-necrosis factor-α (TNF-α) provoke and sustain neuropathic pain.19-21 Oxidative stress has also been implicated in the pathogenesis of small fiber neuropathy.22-24 Nutritional deficits, alcohol, smoking and toxins, such as mercury, arsenic, and lead, can all contribute. For some patients, small fiber neuropathy may be idiopathic with a poorly understood pathogenesis.

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