Small Fiber Neuropathy in hEDS

Small fiber neuropathy (SFN) is one of the most common neurological complications of hypermobile Ehlers-Danlos syndrome (hEDS). It affects the small nerve fibers responsible for transmitting pain and temperature sensations and regulating many automatic body functions, including heart rate, blood pressure, sweating, and digestion.

Research over the past decade has shown that small fiber neuropathy is much more common in people with hEDS than in the general population. It may help explain symptoms such as burning pain, tingling, abnormal sensitivity to touch, dizziness, gastrointestinal problems, and other symptoms that cannot be explained by joint instability alone.

Not everyone with hEDS develops small fiber neuropathy, and symptoms vary considerably from person to person. This article explains what small fiber neuropathy is, its symptoms, how it is diagnosed, and current treatment approaches.

What Is Small Fiber Neuropathy?

Small fiber neuropathy affects the smallest nerves in the peripheral nervous system. These nerves have two primary jobs:

• Carrying pain and temperature sensations to the brain.

• Regulating automatic body functions through the autonomic nervous system.

  
  

Because these nerves serve many different functions, damage to them can affect multiple body systems.

Why this matters: Because routine EMG and nerve conduction studies evaluate large nerve fibers—not the small nerve fibers affected by SFN—these tests are often normal even when small fiber neuropathy is present.

Unlike large fiber neuropathies, small fiber neuropathy usually does not cause muscle weakness or loss of reflexes.

Why Small Fiber Neuropathy Occurs in hEDS

Researchers now know that small fiber neuropathy occurs much more frequently in people with hEDS than in the general population. Skin biopsies have shown that many people with hEDS have a reduced number of small nerve fibers, confirming that SFN is a genuine neurological manifestation of the disorder rather than simply another explanation for chronic pain.

Exactly why this occurs is still unknown. Researchers suspect that several factors contribute, including connective tissue abnormalities surrounding nerves, inflammation, altered blood flow, mast cell activation, immune system dysfunction, and genetics. It is likely that more than one mechanism is involved, and different people may develop SFN for different reasons.

Unlike diabetic neuropathy and many other forms of small fiber neuropathy, SFN in hEDS is often more generalized rather than beginning in the feet and slowly progressing upward. Rather than beginning in the feet and slowly spreading upward, nerve fiber loss in hEDS is often more widespread, suggesting that the disease affects the peripheral nervous system differently than many other neuropathies.

Symptoms

Small fiber neuropathy can affect both sensory nerves and autonomic nerves, so symptoms often involve multiple body systems. Some people experience primarily neuropathic pain, while others have mostly autonomic symptoms. Many have both.

Sensory Symptoms

Common sensory symptoms include

• Burning pain

• Tingling or "pins and needles"

• Electric shock-like sensations

• Stabbing pain

• Pain from normally non-painful touch (allodynia)

• Increased sensitivity to painful stimuli (hyperalgesia)

• Reduced ability to feel pain or temperature

• Numbness

• Neuropathic itch

Some people notice that clothing, bedsheets, or even light touch become painful. Others are particularly sensitive to hot or cold temperatures. Although symptoms often begin in the hands or feet, they may occur anywhere in the body.

Autonomic Symptoms

Because small nerve fibers also regulate many automatic body functions, SFN may contribute to symptoms such as

• Lightheadedness or dizziness

• Rapid heart rate or palpitations

• Heat intolerance

• Abnormal sweating

• Changes in skin color or temperature

• Dry eyes or dry mouth

• Constipation or diarrhea

• Bloating, nausea, or early satiety

• Bladder dysfunction

• Sexual dysfunction

Many of these symptoms overlap with dysautonomia and postural orthostatic tachycardia syndrome (POTS). Current research suggests that small fiber neuropathy contributes to autonomic dysfunction in at least some people with hEDS, although the exact relationship between these conditions is still being studied. For more information, see the Dysautonomia and POTS articles.

What We Still Don't Know

Although researchers have learned a great deal about small fiber neuropathy in hEDS, many important questions remain unanswered.

Important unanswered questions include

• Why some people with hEDS develop small fiber neuropathy while others do not

• Exactly what causes damage to the small nerve fibers

• Whether nerve damage progresses over time or remains relatively stable

• Whether small nerve fibers can regenerate

• Which treatments are most effective for hEDS-associated SFN

• Whether some people may benefit from targeted treatments, such as immunotherapy

As research continues, scientists hope to better understand the biological mechanisms responsible for SFN and develop treatments that target the underlying disease rather than simply relieving symptoms.

Summary

Small fiber neuropathy is increasingly recognized as an important neurological manifestation of hypermobile Ehlers-Danlos syndrome. It affects the small sensory and autonomic nerve fibers responsible for pain, temperature sensation, and many involuntary body functions.

Symptoms vary widely but commonly include burning pain, tingling, abnormal sensitivity to touch, dizziness, gastrointestinal symptoms, and other features of autonomic dysfunction. Because routine EMG and nerve conduction studies are usually normal, diagnosis often requires a skin punch biopsy or other specialized testing.

Although there is currently no treatment that has been proven to reverse hEDS-associated small fiber neuropathy, many people experience meaningful improvement through a comprehensive treatment plan that addresses neuropathic pain, rehabilitation, associated conditions, and overall health.