Small Fiber Neuropathy (SFN) affects the small nerve fibers, causing symptoms like pain, tingling, or numbness. While not exclusively an autoimmune disorder, SFN often has a significant connection to autoimmune conditions.
Understanding Small Fiber Neuropathy
SFN involves damage to the small nerve fibers of the peripheral nervous system, found in the skin and organs. These fibers transmit sensations like pain, temperature, and touch, and regulate automatic bodily functions. Damage to sensory fibers causes burning pain, tingling, or numbness, often starting in the feet and progressing upwards. Autonomic fiber damage can lead to issues like sweating abnormalities, dry eyes/mouth, lightheadedness, or gastrointestinal problems. SFN symptoms often worsen over time.
The Autoimmune Connection to Small Fiber Neuropathy
SFN can be caused by autoimmune conditions where the immune system mistakenly attacks healthy tissues, including small nerve fibers. This leads to inflammation and nerve damage. Identifying an autoimmune cause is important for treatment. Autoimmune diseases linked to SFN include Sjögren’s syndrome, lupus, celiac disease, and sarcoidosis. The presence of autoantibodies, such as TS-HDS or FGFR3, can also indicate an immune-mediated mechanism in unexplained SFN cases.
Beyond Autoimmunity: Other Causes of Small Fiber Neuropathy
While autoimmune conditions are a significant cause, SFN can also stem from other factors. Metabolic conditions like diabetes and prediabetes are frequent causes, affecting up to 50% of individuals. Impaired glucose tolerance is also linked to SFN. Infections (e.g., HIV, Lyme disease), genetic factors (e.g., SCN9A, SCN10A mutations affecting sodium channels), and toxins (e.g., chemotherapy, excessive alcohol) can also induce SFN. About 50% of SFN cases remain idiopathic, meaning without an identified cause.
Diagnosing Small Fiber Neuropathy and Its Underlying Cause
Diagnosing SFN begins with a clinical evaluation, including symptom review and neurological examination. Characteristic symptoms include burning pain, tingling, or numbness, often in a “stocking-glove” pattern. Standard nerve conduction studies are usually normal, as they assess large nerve fibers.
A skin biopsy (epidermal nerve fiber density or ENFD testing) confirms SFN by quantifying small nerve fiber density. Other tests, like Quantitative Sudomotor Axon Reflex Testing (QSART), assess autonomic fiber function. Blood tests screen for underlying causes like autoimmune markers, diabetes, vitamin deficiencies, and infections.
Managing Small Fiber Neuropathy and Its Causes
Managing SFN involves alleviating symptoms and addressing the underlying cause. Symptomatic management focuses on pain control using medications like gabapentin, pregabalin, certain antidepressants, or topical lidocaine creams.
The most effective treatment targets the specific underlying condition. For diabetes-related SFN, strict blood sugar control is essential. Autoimmune causes may require immunosuppressive therapy. Lifestyle modifications, including regular exercise, healthy weight, and a balanced diet, also support nerve health.