Reviews

Office approach to small fiber neuropathy

Author and Disclosure Information

Release date: October 1, 2018
Expiration date: September 30, 2019
Estimated time of completion: 1 hour

Click here to start this CME activity.

Click here to complete post-test and CME certificate.

ABSTRACT

Small fiber neuropathy is often characterized by neuropathic pain in the feet with normal nerve conduction studies and neurologic examination. Diagnosis requires specialized nerve tests, including autonomic studies and a skin biopsy study showing reduced intraepidermal nerve fiber density. Small fiber neuropathy has numerous causes but is often idiopathic. A practical approach to identifying an underlying cause is to first screen for common ones and then proceed with further testing as needed. Treatment consists of correcting the underlying cause, managing pain, and modifying lifestyle.

KEY POINTS

  • Patients typically develop a symmetric “stocking-glove” pattern of sensory loss in the feet and hands.
  • The diagnosis may be confirmed with skin biopsy for nerve fiber density, which can easily be done in a clinic setting with commercially available kits.
  • Diabetes is the most common identifiable cause of small fiber neuropathy.
  • Serologic testing can help uncover a vitamin deficiency or other potentially treatable condition.
  • Antiepileptics, antidepressants, and topical agents are first-line drugs for managing pain.


 

References

Peripheral neuropathy is the most common reason for an outpatient neurology visit in the United States and accounts for over $10 billion in healthcare spending each year.1,2 When the disorder affects only small, thinly myelinated or unmyelinated nerve fibers, it is referred to as small fiber neuropathy, which commonly presents as numbness and burning pain in the feet.

This article details the manifestations and evaluation of small fiber neuropathy, with an eye toward diagnosing an underlying cause amenable to treatment.

OLDER PATIENTS MOST AFFECTED

The epidemiology of small fiber neuropathy is not well established. It occurs more commonly in older patients, but data are mixed on prevalence by sex.3–6 In a Dutch study,3 the overall prevalence was at least 53 cases per 100,000, with the highest rate in men over age 65.

CHARACTERISTIC SENSORY DISTURBANCES

Table 1. Features of small fiber neuropathy
Characteristic clinical features are summarized in Table 1.

Sensations vary in quality and time

Patients with small fiber neuropathy typically present with a symmetric length-dependent (“stocking-glove”) distribution of sensory changes, starting in the feet and gradually ascending up the legs and then to the hands.

Commonly reported neuropathic symptoms include various combinations of burning, numbness, tingling, itching, sunburn-like, and frostbite-like sensations. Nonneuropathic symptoms may include tightness, a vise-like squeezing of the feet, and the sensation of a sock rolled up at the end of the shoe. Cramps or spasms may also be reported but rarely occur in isolation.7

Symptoms are typically worse at the end of the day and while sitting or lying down at night. They can arise spontaneously but may also be triggered by something as minor as the touch of clothing or cool air against the skin. Bedsheet sensitivity of the feet is reported so often that it is used as an outcome measure in clinical trials. Symptoms can also be exacer­bated by extremes in ambient temperature and are especially worse in cold weather.

Random patterns suggest an immune cause

Symptoms may also have a non–length-dependent distribution that is asymmetric, patchy, intermittent, and migratory, and can involve the face, proximal limbs, and trunk. Symptoms may vary throughout the day, eg, starting with electric-shock sensations on one side of the face, followed by perineal numbness and then tingling in the arms lasting for a few minutes to several hours. While such patterns may be seen with diabetes and other common etiologies, they often suggest an underlying immune-mediated disorder such as Sjögren syndrome or sarcoidosis.8–10 Although large fiber polyneuropathy may also be non–length-dependent, the deficits are usually fixed, with no migratory component.

Autonomic features may be prominent

Autonomic symptoms occur in nearly half of patients and can be as troublesome as neuropathic pain.3 Small nerve fibers mediate somatic and autonomic functions, an evolutionary link that may reflect visceral defense mechanisms responding to pain as a signal of danger.11 This may help explain the multi­systemic nature of symptoms, which can include sweating abnormalities, bowel and bladder disturbances, dry eyes, dry mouth, gastrointestinal dysmotility, skin changes (eg, discoloration, loss of hair, shiny skin), sexual dysfunction, orthostatic hypotension, and palpitations. In some cases, isolated dysautonomia may be seen.

TARGETED EXAMINATION

History: Medications, alcohol, infections

When a patient presents with neuropathic pain in the feet, a detailed history should be obtained, including alcohol use, family history of neuropathy, and use of neurotoxic medications such as metronidazole, colchicine, and chemotherapeutic agents.

Human immunodeficiency virus (HIV) and hepatitis C infection are well known to be associated with small fiber neuropathy, so relevant risk factors (eg, blood transfusions, sexual history, intravenous drug use) should be asked about. Recent illnesses and vaccinations are another important line of questioning, as a small-fiber variant of Guillain-Barré syndrome has been described.12

Assess reflexes, strength, sensation

On physical examination, particular attention should be focused on searching for abnormalities indicating large nerve fiber involvement (eg, absent deep tendon reflexes, weakness of the toes). However, absent ankle deep tendon reflexes and reduced vibratory sense may also occur in healthy elderly people.

Similarly, proprioception, motor strength, balance, and vibratory sensation are functions of large myelinated nerve fibers, and thus remain unaffected in patients with only small fiber neuropathy.

Evidence of a systemic disorder should also be sought, as it may indicate an underlying etiology.

Pages

Next Article:

Small fibers, large impact

Related Articles