At The London Clinic, we offer a unique service to help diagnose small fibre neuropathy as part of our neurology speciality.

Definition:

Small fibre neuropathy is a type of neuropathy affecting small nerve fibres of the peripheral nervous system. The function of these fibres is to carry the sensation of temperature and pain, as well as to help control the function of the sweat glands, gastrointestinal organs, blood vessels and heart. The incidence and prevalence is not known but the number of patients with small fibre neuropathy has been increasing as the awareness of the condition has risen in the world.

Symptoms:

  • Small fibre neuropathy typically causes painful and burning sensation, often in the feet, but also in other parts of the body including arms, face and trunk.
  • The pain is usually constant but can vary throughout the day and it can be worse during rest or at night.
  • The patients are sensitive to touch and may get pain from bed sheets touching their feet. Patients may also report transient electric shock-like pain lasting for seconds but many times during the day. Cramps can also occur.
  • Patients also report light headedness, a drop in blood pressure when standing, feeling faint, abnormal sweating, gastrointestinal and sexual dysfunction.
  • Patients with small fibre neuropathy may be misdiagnosed as having a plantar fasciitis, fibromyalgia or psychosomatic syndrome.

Examination and diagnosis:

Neurological examination of patients with small fibre neuropathy is often normal, although some patients may have decreased pinprick or temperature sensation or heightened sensitivity to pain.

Skin can be dry, cracked or shiny in affected areas. Postural blood pressure drop with a resting fast pulse may be seen in patients.

Nerve conduction studies in small fibre neuropathy are normal but they should be done to establish whether the patient has a large fibre neuropathy as this may help with diagnostic process.

Skin biopsy:

Until recently there was no objective test to help establish the diagnosis of the small fibre neuropathy. This has significantly changed in the last ten years with the introduction of the measurement of intraepidermal nerve fibre density. The test is done by taking a skin biopsy.

A skin biopsy is typically conducted at two sites: 10 cm above the right outer ankle and 20cm below right outer hip joint. The procedure involves using a local anaesthetic and then taking two 3mm punch skin biopsies. The biopsy sites are closed with steristrips and covered with a dressing, which should be removed in 7 days. The biopsy site should not hurt but if necessary the patients can take Paracetamol or Ibuprofen.

Causes:

If the skin biopsy confirms small fibre neuropathy, your consultant will look for the cause which can be identified in around 50% cases. Small fibre neuropathy is associated with a number of common diseases such as diabetes or metabolic syndrome (hyperlipidemia, hypertension, obesity and abnormal glucose metabolism). It can be also seen in patients with abnormal thyroid function, vitamin B12 deficiency or chronic kidney disease.

Other conditions associated with small fibre neuropathy include immune disorders such as Sjogren’s syndrome, systemic lupus erythematosus, rheumatoid arthritis, sarcoid, coeliac disease, paraproteinemia, amyloid, inflammatory bowel disease, paraneoplastic syndromes, and infections such as hepatitis C or HIV, neurotoxic drug use (anti-retrovirals, antibiotics – Metronidazole, Nitrofurantoin, Linezolid, chemotherapy – Bortezomib, Flecainide, statins, alcohol, excess vitamin B6). Small fibre neuropathy can be genetic as a part of Fabry disease.

Management:

Once the treatable cause has been identified, your treatment should focus on treating the cause.

Appropriate control of diabetes can halt the progression of small fibre neuropathy. Treatment of hepatitis C will restore the intraepidermal nerve fibre density and improve the pain. Intravenous immunoglobulins can reduce the pain in patients with Sjogren’s syndrome. Unfortunately treatment of HIV will not alter the progression of small fibre neuropathy.

There are no specific guidelines for management of pain associated with small fibre neuropathy although consensus guidelines for neuropathic pain have been adapted for pain management associated with small fibre neuropathy. Your consultant will advise on this.