Small fiber peripheral neuropathy
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|Small fiber peripheral neuropathy|
|Classification and external resources|
|ICD-10||G63.3 G60.8 G62.8|
Small fiber peripheral neuropathy is a type of peripheral neuropathy that occurs from damage to the small unmyelinated peripheral nerve fibers. These fibers, categorized as C fibers, are present in skin, peripheral nerves, and organs. The role of these nerves is to innervate the skin (somatic fibers) and help control autonomic function (autonomic fibers). It is estimated that 15-20 million people in the United States suffer from some form of peripheral neuropathy.
Sensory symptoms of small fiber neuropathy are highly variable. Common complaints include paresthesias, dysesthesias, and insensitivity to pain. Paresthesias are abnormal sensations. They are often described as numbness, burning, cold, prickling, pins and needles along with other symptoms. Dysesthesias are unpleasant sensations, either spontaneous or evoked. A light breeze, the feeling of clothes, or even a soft touch can cause pain. Insensitivity to pain can be particular problem. One may be bleeding or have a skin injury without even knowing it.
Like many polyneuropathies, the symptoms usually start in the longer nerves and progressively attack shorter nerves. This means that most often the symptoms start in the feet and progress upwards, and usually symptoms are more severe in the feet. However, patients with Fabry disease have isolated small fiber engagement, and can have a more widespread small fiber disruption.
This neuropathy is considered a separate clinical entity from a regular large-fiber polyneuropathy. Small fibers are difficult to diagnose. The diagnosis of a large-fiber (common) polyneuropathy is much easier. Many large-fiber polyneuropathies have minor small-fiber engagement, and small-fiber engagements are often implied if the patient has minor small-fiber symptoms in addition to large-fiber symptoms. The clinical picture of an isolated small-fiber neuropathy is characteristic, but the diagnosis is not always easy.
Nerve conduction tests and electromyography (EMG tests), which are used to diagnose other neuropathies, are ineffective in detecting small fiber neuropathies. Quantitative sensory testing (QST) can be used to measure more objective changes in the temperature sensation. An elevated heat-detection threshold, heat-pain threshold, a reduced cold detection threshold or cold pain threshold may indicate a small-fiber neuropathy. A conventional nerve biopsy is not useful, since in this procedure mostly large-fiber nerves are studied. A skin biopsy (with the measurement of intraepidermal nerve fiber density) can be used for a diagnosis, but is not commonly available. This test allows for direct visualization of the un-myelinated nerve fibers (the "small fibers") in the epidermal layer of the skin, and requires taking a small skin sample.
A Thermoregulatory Sweat Test is a test used by specialized clinics e.g. Mayo Clinic in Rochester, MN. A powder that changes color with sweating is applied all over the body, but spares the face. If the patient sweats normally the indicator powder changes to a purple color. Locations that change in color to an orange or yellowish color can indicate where there is small fiber neuropathy.
There are many possible causes of small fiber neuropathy. The most common cause is diabetes or glucose intolerance. Other possible causes include hypothyroidism, Sjögren's syndrome, Lupus, vasculitis, sarcoidosis, nutritional deficiency, Celiac disease, Lyme disease, HIV, Fabry disease, amyloidosis and alcoholism. A 2008 study reported that in approximately 40% of patients no cause could be determined after initial evaluation. When no cause can be identified, the neuropathy is called idiopathic. A recent study revealed dysfunction of a particular sodium channel (Nav1.7) in a significant portion of the patient population with an idiopathic small fiber neuropathy.
Recently several studies have suggested an association between autonomic small fiber neuropathy and postural orthostatic tachycardia syndrome. Other notable studies have shown a link between Erythromelalgia, and Fibromyalgia
||The examples and perspective in this section deal primarily with USA and do not represent a worldwide view of the subject. (December 2010)|
Treatment is based on the underlying cause, if any. Where the likely underlying condition is known, treatment of this condition is indicated treated to reduce progression of the disease and symptoms. For cases without those conditions, there is only symptomatic treatment.
There is a treatment called Transvascular Autonomic Modulation (TVAM) that restores autonomic function to patients with fibromyalgia. The procedural goal of TVAM is to stimulate the autonomic nerve fibers surrounding the central veins. This stimulation leads to a reset in the hypothalamus. The result is improved autonomic ‘tone’. By restoring the body’s ability to internally regulate, the above symptoms can be reduced or eliminated, vastly improving the quality of life for many patients.
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- Faber, C, et al. (2011). "Gain of function Na(V) 1.7 mutations in idiopathic small fiber neuropathy". Annals of Neurology.