For the pain sufferer…

Patient FAQ

Some patients come to us with questions about small fiber neuropathy (SFN) and epidermal nerve fiber density (ENFD) testing. We at CRL are dedicated to providing complete information so patients may better understand the process of diagnoses through small fiber neuropathy testing. The following answers to the most frequently asked questions will help patients better understand the skin biopsy that was performed by their medical provider.

If you have a medical emergency, please dial 911 or contact your medical provider immediately.
What is Small Fiber Neuropathy (SFN)?

Our nerves are made up of fibers of varying sizes, ranging from small fibers which sense pain and temperature to large fibers which assist in our sense of balance. Small fiber neuropathy results from damage to the small, unmyelinated nerve fibers that convey pain and temperature sensations from receptors in the skin. Small fiber peripheral neuropathy is a type of peripheral neuropathy. This condition is also called small fiber neuropathy, small fiber sensory neuropathy (SFSN), and C fiber neuropathy. If there is damage to the small nerve fibers near the skin’s surface, patients can experience problems with pain, burning, stabbing, or numbness. Usually the symptoms start in the feet and lower legs, although they may begin in the torso or face.

Until relatively recently, small fiber neuropathy has been diagnosed mainly by excluding other conditions. Tests such as Electromyography and Nerve Conduction Studies (EMG/NCV) are accurate at diagnosing most forms of neuropathy. However, results will come back as normal in people with isolated small fiber neuropathies. Currently, the small nerve fibers in the skin can be analyzed by means of a simple skin biopsy.

What are the Symptoms of SFN?

The most common symptoms associated with small fiber neuropathy are tingling, burning, numbness and pain.

What Causes SFN?

While the exact cause of small fiber neuropathy for many patients often remains a mystery, in some patients small fiber neuropathies can be caused by disorders of metabolism such as diabetes, chronic infections (such as human immunodeficiency virus), genetic abnormalities, toxicity from various drugs, impaired glucose tolerance (IGT), and autoimmune diseases.

How is small fiber neuropathy diagnosed?

Your physician will diagnose small fiber neuropathy by means of a skin biopsy. This is a simple procedure in which a small circular piece of skin (a punch biopsy, smaller than the diameter of a pencil eraser) is taken from the surface of the skin. Lidocaine, a local anesthetic, is used to numb the skin first. This involves just a small needle poke. A band-aid is placed over the biopsy site, no stitches are involved, and it heals simply by scabbing over. The whole procedure takes only a few minutes. The skin specimen is processed and sent to Corinthian Reference Lab in a special way so that the small nerve fibers in the skin can be visualized and counted by qualified neuromuscular neurologists and dermatopathologists.

Why Should I Undergo Small Fiber Neuropathy (SFN) Testing?

The only way to definitively diagnose small fiber neuropathy is through a skin biopsy. Small Fiber Neuropathy is often undiagnosed. A confirmed diagnosis is important for many reasons. There are several treatment options for SFN, so a confirmed diagnosis can be helpful in determining the best management strategy. A confirmed diagnosis can also be helpful for those patients seeking disability insurance. It is important to note that testing for SFN is covered by most insurance companies.

Why did my physician perform this biopsy?

Small fiber neuropathy results from damage to the small, unmyelinated nerve fibers that convey pain and temperature sensations. Routine neurological exams such as EMG and nerve conduction studies can often be normal in patients with isolated small fiber neuropathy. The physician performs a skin biopsy to more accurately diagnose a problem with the small nerve fibers. A skin biopsy followed by epidermal nerve fiber density testing can be the only way to make a diagnosis of small fiber neuropathy. CRL performs epidermal nerve fiber density testing, a process in which nerves are counted to more accurately diagnose small fiber neuropathy. CRL offers patients objective evidence of a neuropathy which can hopefully lead to a more precise diagnosis and treatment. ENFD testing is the most sensitive test available to aid in the diagnosis of small fiber neuropathy.

What does the Test Show?

The skin is processed and placed on a slide allowing one of our highly trained neurologists or pathologists to count the nerve fibers. If the number of fibers is less than a certain value, a diagnosis of small fiber neuropathy is made. Arrows below point to the nerve fibers in the skin.

What are the Available Treatment Options?

The treatment for small fiber neuropathy depends on whether or not a cause can be identified. In cases where neuropathy is caused by diabetes or toxins, treatment of these underlying conditions may reduce progression of the disease and its symptoms. If no cause is identified, treatment focuses on techniques to decrease the pain or other symptoms. The ability to diagnosis patients with SFN with a relatively non-invasive skin biopsy has opened up this area to research, hopefully resulting in new treatment options.

Will I need a repeat biopsy and if so why?

A repeat biopsy can often be ordered by a physician to track the progress of a patient’s disease and/or therapy. Small fiber nerves can regrow if the disease process is halted. The regrowth of these small nerves can happen within months, which is significantly faster than larger nerves tend to re-grow. In addition, a patient’s symptoms may change over time. Because ENFD testing is the only way to objectively measure the change in the number of small fibers, a repeat biopsy can be helpful to the physician.

What is Corinthian Reference Lab (CRL)?

Corinthian Reference Lab specializes in Epidermal Nerve Fiber Density (ENFD) testing. Your physician has chosen CRL for its expertise in performing this very specific, labor intensive test. Specimens require extensive manual manipulation and nerve fibers are counted individually. All of our specimens are read by neuromuscular neurologists and by a dermatopathologist to provide the most specialized interpretations of the patient’s specimen. For more information on our lab and team of experienced professionals and clinicians, please see our about us page.

How will I get my Lab Results?

Your results will be sent directly to your physician within two weeks of your biopsy. We cannot discuss the test results directly with the patient: the results of your ENFD test must be discussed with the referring physician. Please remember to schedule your follow up appointment with your physician to receive the results.

SFN Testing Information

What is the procedure like?

The explanation to your unexplained numbness is probably just a 3 millimeter skin sample away! Your doctor can take the sample and send it to our experts for review, and YOU can get the answers you’ve been waiting for all this time.