What is small fiber neuropathy?
Small fiber neuropathy is a type of neuropathy caused by damage to the small, unmyelinated fibers in the peripheral nerves that innervate the skin and other organs. These fibers carry pain and temperature sensations from the skin, and mediate autonomic functions. Dysfunction of the small nerve fibers can cause sensory or autonomic symptoms.
Making the diagnosis of small fiber neuropathy will provide details in directing treatment plans for potentially reversible causes, which can result in amelioration of the neuropathy.
What are the signs of small fiber neuropathy?
Symptoms of sensory small fiber neuropathy include numbness, hypersensitivity, and spontaneous painful or abnormal sensations such as tingling, burning, freezing, stabbing, itching, tearing, aching, or electric sensations that fluctuate in severity throughout the day. Most people describe their symptoms as pins and needles. The skin can also be hypersensitive to pressure or touch.
Symptoms of autonomic small fiber neuropathy include abnormal sweating or temperature regulation, light-headedness or fainting, bloating, incomplete bladder emptying, dryness and thinning of the skin and possibly hair loss in the legs.
What are the causes of small fiber neuropathy?
The causes of small fiber neuropathy are diverse. The most common cause is diabetes mellitus or glucose intolerance, metabolic syndrome, thyroid dysfunction, Sjögren’s syndrome, lupus, psoriasis and other unspecified inflammatory conditions. In cases where no cause can be found, the neuropathy is called idiopathic.
Is there a treatment for small fiber neuropathy?
The main therapeutic intervention in patients with small fiber neuropathy is symptomatic treatment for the neuropathic pain. Therapy is directed at both the underlying cause, if one can be identified, and at ameliorating the symptoms.
Many medications can be used, standard first-line therapies such as duloxetine (Cymbalta, Lilly), pregabalin (Lyrica, Pfizer), and gabapentin (Neurontin, Pfizer) have proven useful. Additional treatment options include other anti-seizure and antidepressant medications.
Why do I need a skin biopsy to diagnose small fiber sensory neuropathy?
Small fibers typically travel too slow and their conduction responses cannot be studied by conventional nerve conduction study or EMG tests, which are routinely performed to evaluate for large sensory and motor neuropathy. Therefore, skin biopsy is used to evaluate small sensory nerve fibers in the skin.
Is skin biopsy a very invasive procedure?
No, it is considered a minimally invasive procedure. We routinely do skin biopsy on 1 side at 2 different sites, above the ankle and below the hip using a 3 mm (diameter) biopsy punch. No stitches are required since the biopsy size is so small. The biopsy sites will be healed within 1 week, but will leave small scars. The whole procedure takes about 10–15 minutes. Lidocaine injection around the biopsy site will be used to numb your skin. The procedure is very well tolerated.
Who performs these tests?
These tests must only be performed by highly specialized physicians, with extra training in clinical neurophysiology or neuromuscular disorders. Both, Dr Yono and Dr Kashouty have subspecialty training and are highly qualified to perform these procedures.
No special preparation is needed. Make sure you take your usual medications unless instructed otherwise. You will generally be ready to go home immediately following the test.