Small Fiber Neuropathy (SFN)

Understanding SFN

Small fiber neuropathy (SFN), a type of peripheral neuropathy, results from damage to certain small peripheral nerve fibers (ones protected with a covering called myelin) found in the skin, peripheral nerves and internal organs.

Symptoms of SFN

The signs and symptoms of small fiber neuropathy (SFN) usually begin in adolescence to mid-adulthood. SFN is characterized by severe pain attacks that typically begin in the feet or hands. Depending on which small nerve fibers are affected, symptoms can vary. Some individuals experience a more generalized, whole-body pain. The attacks usually consist of pain described as stabbing or burning, or abnormal skin sensations such as tingling or itchiness. In some individuals, the pain is more severe during times of rest or at night.

Individuals with SFN cannot feel pain that is concentrated in a very small area, such as the prick of a pin. However, they have an increased sensitivity to pain in general and experience pain from stimulation that typically does not cause pain. Individuals affected with this condition may also have a reduced ability to differentiate between hot and cold while in others, the pain attacks are caused by cold or warm triggers.

Some individuals have urinary or bowel problems, episodes of rapid heartbeat (palpitations), dry eyes or mouth, or abnormal sweating. They can also experience a sharp drop in blood pressure upon standing (orthostatic hypotension), which can cause dizziness, blurred vision, or fainting.

Diagnosing SFN

Small fiber neuropathy (SFN) may be caused by a genetic problem or another health condition such as diabetes mellitus. In fact, 6 to 50% of diabetics or pre-diabetics develop SFN. Diagnosis is based on history, clinical examination and supporting laboratory investigations. Electromyography and nerve conduction studies are done to eliminate other conditions. Skin biopsies are used to confirm small nerve fiber density.

Treatment of SFN

There is no cure for small fiber neuropathy (SFN). Treatment includes managing symptoms as well as the underlying cause. If SFN is caused by diabetes, then the treatment is aimed at correcting the diabetes (for example, through diet, exercise and/or diabetes medication). SFN may be caused by an autoimmune problem, which is when the immune system malfunctions and creates antibodies that attack and cause damage to a part of the body (in this case, the nerve fibers). If this is suspected, a treatment option is immune globulin therapy administered into the blood stream intravenously (IVIG).

References:

• Small Fiber Neuropathy | Medline Plus
• Small Fiber Sensory Neuropathy | Johns Hopkins Medicine
• Liu X, Treister R, Lang M, Oaklander AL. IVIg for apparently autoimmune small-fiber polyneuropathy: first analysis of efficacy and safety. Ther Adv Neurol Disord. 2018;11:1756285617744484. Published 2018 Jan 8. doi:10.1177/1756285617744484