Small fiber neuropathy: What is it?

Definition

Have you ever stubbed your toe and experienced a shocking feeling running through your body or sat on your leg for so long that it went numb for a moment? Sensory nerves are the ones to “blame” for those sensations. They regulate the body’s senses and help navigate daily life. Small fiber neuropathy (SFN) causes damage to these nerves, inflicting pain and complicating the patient’s life.

Chronic neuropathic pain affects over 7% of the general population, potentially causing serious quality-of-life limitations. One of the peripheral neuropathic conditions is small fiber neuropathy (SFN). The condition is commonly accompanied by other illnesses and chronic diseases or can be manifested in the patient’s life on its own. SFN impacts the peripheral nerve system, which links the brain and spinal cord to muscles and cells that receive sensations including touch, smell, and pain. The condition influences the transmission of pain and temperature from the skin to the brain, resulting in sharp pain as the primary symptom. Many patients describe the pain from small fiber neuropathy as electroshocking, stabbing or burning. Luckily, since the condition is widely caused by other illnesses, treating the underlying condition can ease SFN symptoms. Previously the research regarding small fiber neuropathy was concentrated on adults, however now it is known that many children suffer from the condition as well. Most people living with small fiber neuropathy are over 65 years of age and are predominantly male.

Symptoms

The symptoms of small fiber neuropathy can vary from patient to patient; however, the first signs of the conditions are often:

• Burning pain,
• Tingling sensations in the feet,
• Numbness in the feet and hands.

The symptoms can spread to other areas of the body over time as well as intensify, causing more discomfort. Other symptoms of small fiber neuropathy can include:

• Excessive sweating,
• Digestive problems,
• Sexual issues,
• Stiffness in the hands or feet,
• Urinary difficulties,
• Dizziness,
• Brain fogginess,
• Redness of the skin.

Causes

Small fiber neuropathy can be caused by a variety of factors. According to the American Academy of Neurology, 50% of patients with diabetic or prediabetic conditions also develop small fiber neuropathy. Other causes of SFN may include:

• Metabolic and endocrine disorders: Hypothyroidism, vitamin B12 deficiency,
• Autoimmune disorders: Sjogren’s syndrome, Lupus,
• Infectious conditions: HIV, Lyme disease,
• Exposure to certain toxins: Chemotherapy drugs and heavy metals,
• Alcohol or drug abuse.

The risk of cardiovascular issues can be increased due to these chronic conditions, or comorbidities. In consequence, this may have an impact on a person's general well-being and lifespan.

The cause of small fiber neuropathy in children and teens is predominantly autoimmune diseases. It is vital to know that the effects of small fiber neuropathy on children are not as well-known or studied as much as the effects on adults since the condition was widely associated only with old age until recently.

However, the underlying illness is not always the cause of small fiber neuropathy occurrence. A 2018 study shows that up to 53% of people with SFN have no additional condition. In cases, when small fiber neuropathy develops on its own, it is called idiopathic. The term "idiopathic," in definition, means “no cause”. Dealing with idiopathic small fiber neuropathy can be challenging for both patients and doctors, as it is not the easiest to diagnose or treat correctly. Thankfully, due to more in-depth research and new technologies, idiopathic small fiber neuropathy treatments are progressing year after year.

Diagnosis

Physical examination, nerve conduction tests, and skin biopsies to determine the density of small nerve fibers in the body are all methods used to diagnose small fiber neuropathy. The diagnosis process can be quite long for most patients. However, early diagnosis is very important to manage the symptoms of SFN and ensure the best-personalized treatment.

Physical examination

A technique to determine sensory neuropathy is called quantitative sensory testing (QST). These regulated and controlled sensory tests including stimulation, vibration, and temperature, can identify both small fiber and large fiber neuropathies. Nevertheless, quantitative sensory testing has imperfections, and the results can have a margin of error. For example, anomalies in either the central or peripheral neural systems can affect the legitimacy of the results. In addition, quantitative sensory testing is not able to detect the difference between both fabricated and genuine loss of feeling.

Nerve conduction test

Diagnostic techniques like nerve conduction studies (NCS) and electromyography (EMG) can be crucial to identifying small fiber neuropathy. These tests are able to measure the activity of the sensory nerves in different ways. Little electrodes are inserted into the muscles as part of the EMG process to detect electrical activity, whereas NCS analyses the strength and speed of nerve impulses as they move from one location to another. These examinations might spot changes in nerve activity that might be signs of small fiber neuropathy, such as slowed nerve conduction velocity or irregular muscle action.

Skin biopsy

Skin biopsy is necessary to diagnose small fiber neuropathy, as it is the method that can track the activity of small fibers most accurately. During the procedure, local anesthetic is used to remove a small amount of skin tissue, usually from the ankle. The density of tiny sensory neurons in the skin is then assessed by microscopically examining the tissue. Small fiber neuropathy is indicated by a decrease in the density of tiny nerve fibers. This method can be carried out in a clinical environment and is not as invasive as it may sound.

Treatment

There are many treatment options for small fiber neuropathy, depending on the severity of the illness and underlying conditions of each patient. Here are some of the treatment options for small fiber neuropathy:

To cope with moderate pain, pain relievers such as acetaminophen or nonsteroidal anti-inflammatory drugs (NSAIDs) can often be prescribed. Neuropathic pain can also be effectively treated with anticonvulsant medications like gabapentin or pregabalin.

Opioids or other stronger painkillers may be recommended for more severe pain, but due to the possibility of addiction and other side effects, these should only be taken with extreme caution.

Several additional drugs can be used to treat small fiber neuropathy in combination with painkillers. Antidepressants like amitriptyline or duloxetine can be used to boost the patient’s mood and help with symptoms management.

To relieve the symptoms, topical analgesics can be applied directly to the affected area, such as capsaicin cream or lidocaine patches.

In addition to medical treatments, living a healthy lifestyle, eating fewer processed foods, exercising on a regular basis and getting enough sleep can help to deal with the symptoms of small fiber neuropathy.