Small Fiber Neuropathy
Small fiber neuropathy (SFN) affects the small unmyelinated C-fibers and thinly myelinated A-delta fibers responsible for pain, temperature, and autonomic function. Standard nerve conduction studies often appear normal, making skin biopsy the diagnostic gold standard.
Key Takeaways
- SFN affects pain, temperature, and autonomic nerve fibers.
- Standard EMG and nerve conduction studies are typically normal.
- Skin biopsy showing reduced nerve fiber density confirms the diagnosis.
- Common causes include diabetes, prediabetes, and autoimmune conditions.
- Treatment focuses on the underlying cause and symptom management.
Frequently Asked Questions
- What is small fiber neuropathy?
- Small fiber neuropathy (SFN) is damage to the small unmyelinated C-fibers and thinly myelinated A-delta fibers that carry pain, temperature, and autonomic signals. Symptoms include burning pain, tingling, sensitivity to touch, and autonomic problems such as abnormal sweating, dry eyes, palpitations, or lightheadedness.
- How is small fiber neuropathy diagnosed?
- Because standard nerve conduction studies test large fibers and are usually normal in SFN, diagnosis relies on a punch skin biopsy from the lower leg that measures intraepidermal nerve fiber density. Quantitative sensory testing and autonomic function testing are also used.
- What causes small fiber neuropathy?
- Common causes include diabetes and prediabetes, autoimmune disorders (Sjögren's syndrome, sarcoidosis, celiac disease), thyroid disease, vitamin B12 deficiency, certain infections, and genetic causes such as sodium channel mutations. About 30–50% of cases are idiopathic at initial workup.
- Is small fiber neuropathy serious?
- It is rarely life-threatening, but it can cause significant pain and autonomic symptoms that affect quality of life. Identifying and treating an underlying cause — such as glucose control or immunotherapy for autoimmune disease — can stabilize or improve symptoms in some patients.