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Small-Fiber Neuropathy: Answering the Burning Questions

Small-fiber neuropathy is a peripheral nerve disease that most commonly presents in middle-aged and older people, who develop burning pain in their feet. Although it can be caused by disorders of metabolism such as diabetes, chronic infections (such as with human immunodeficiency virus), genetic abnormalities, toxicity from various drugs, and autoimmune diseases, the cause often remains a mystery because standard electrophysiologic tests for nerve injury do not detect small-fiber function.

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Articles of Interest

Small Fiber Neuropathy

SFN is a common type of peripheral neuropathy that predominantly affects small, myelinated Aδ fibers and unmyelinated C fibers. SFN can affect somatic sensory fibers and autonomic C fibers, and most people with SFN have predominantly somatic sensory involvement that is often painful, especially when associated with amyloidosis, diabetes mellitus, HIV, sarcoidosis, sodium channelopathy, alcohol toxicity, and neurotoxic drug exposure.

Small Fiber Neuropathy Overview

The causes of small fiber neuropathy are diverse, and in some cases, the neuropathy is the first manifestation of an underlying systemic disease. The most common cause is diabetes mellitus or glucose intolerance.

Small fiber neuropathy: a common and important clinical disorder

SFN is a relatively common disorder resulting in severe and troublesome symptoms, which may be difficult to control. Standard electrophysiological tests such as nerve conduction studies and EMG remain normal in SFN. Therefore, the syndrome may easily be overlooked.

Small Fiber Versus Large Fiber Neuropathies

Nerve fibers are classified based on their thickness into small fibers and large fibers depending on how thick they are. Large fiber nerve cells have diameters more than about 5 micrometers, and small fibers are thinner. The large fibers are bigger because the axons are sheathed in fatty wrappings called “myelin”. This helps them to send signals faster than small-fibers can. Large fibers carry messages to the muscles to control our movements. They also receive and carry some sensations to the spinal cord and brain including touch, vibration, and balance. The small fibers send messages about illness and injury, including pain and itch and hot and cold. “Autonomic” small fibers also carry messages that control our internal organs.

Understanding Small Fiber Neuropathy

Millions suffer from small fiber neuropathy, a medical condition that occurs when the small fibers of the peripheral nervous system are damaged. It is often caused by an underlying health condition such as diabetes. Small fiber neuropathy can be debilitating, but the good news is that often, once the underlying health condition is identified and treated, it gets better.

Resources

Understanding B6 Toxicity

B6 toxicity is Small Fiber Polyneuropathy (SFPN). Small Fiber Polyneuropathy is also called Small Fiber Neuropathy as well as Peripheral Neuropathy. We know through the research done at Massachusetts General Hospital by Dr. Anne Oaklander that B6 is one of the causes of Small Fiber Polyneuropathy.

StatPearls

Small fiber neuropathy presents with burning pain, often beginning in the extremities, most notably in the feet. It is due to the involvement of A-delta and C nerve fibers. It may occur idiopathically or due to metabolic, hereditary, infectious, immune-mediated, or toxic etiologies.