Many neuropathy patients have heard these words, “Your EMG and Nerve Conduct Studies are normal meaning you do not have neuropathy.” Right? Wrong.
Dr. Norman Latov of Cornell University states clearly along with many other professionals that the EMG and Nerve Conduct Studies only measure damage to the large fibers. In fact it is well known that a patient can have symptoms of Peripheral Neuropathy long before damage is done to either the large or small fiber nerves! Plus small fiber damage can only be measured by a simple Skin Biopsy to determine if the patient has damage to the small fibers.
David Saperstein M.D. and Todd Levine M.D. write for the GBS/CIDP Foundation International in Summer 2012 in The Communicator: “Immune-Mediated Small Fiber Neuropathy: A Treatable Condition That Can Mimic GBS and CIDP” . The authors note that “some patients may have elevated spinal fluid protein levels as in (GBS and CIDP), while other patients will have evidence of a monoclonal protein in their blood (which can be associated with some kinds of CIDP) and note that acute onset SFN can be immune-mediated and may respond to the same therapies used for GBS, such as intravenous immunoglobulin (IVIg). In contrast to GBS, however patients with acute onset SFN may respond to corticosteroid medications such as prednisone.” The doctors continue with a recommendation that the skin biopsy is a very useful tool in the diagnosis of SFN.
Small Fiber Neuropathy
Small fiber neuropathies affect the small, unmyelinated nerve fibers in the sensory nerves. These fibers convey pain and temperature sensations from the skin, as well as maintain autonomic functions (Stewart el al, 1992; Novak et al 2001). The diagnosis can easily be missed, as the neurological examination may reveal only minor sensory abnormalities and EMG and nerve conduction studies, that measure the large fibers, are frequently normal. Consequently, some patients with small fiber neuropathy are misdiagnosed as having a psychosomatic disorder, RSD, fibromyalgia, or restless leg syndrome instead. (Lacomia, 2002; Hermann et al, 2004; Polydefkis et al, 2005).
Symptoms of Small Fiber Neuropathy
Symptoms of small fiber neuropathy include numbness and annoying or painful spontaneous sensations, called paresthesias, that are variably described as tingling, stinging, burning, freezing, itching, aching, pulling, squeezing, or electric shock-like in character. Innocuous stimuli can provoke unpleasant sensations, called dysesthesias, as when clothes feel like sandpaper against the skin, the hands are hypersensitive to touch, and pressure from shoes or socks causes severe pain. These symptoms can occur anywhere in the body, including the arms, legs, torso, face, or even the mouth. (Walk et al, 2003; Lauria et al. 2005)
Causes of Small Fiber Neuropathy
Small fiber neuropathy can result from a number of causes and the neuropathy is often the first manifestation of an underlying systemic disease. It can be caused by diabetes mellitus or glucose intolerance (Polydefkis and McArthur, 2005) and by such autoimmune conditions as Sjogren’s syndrome (Chat et al, 2005) Lupus (Omdal et al, 2002), sarcoid (Hoitsman et al, 2005) vasculitis (Lacomis et al, 1997; Zafrir et al, 2004) Lee et al, 2005), inflammatory bowel disease (Gondim et al. 2005) or variants of Guillain-Barre syndrome (Seneviraine and Gunasekera, 2002). Other causes include nutritional deficiencies, celiac disease (Brannagan et al, 2005), Lyme disease, HIV-1 infection (Polydefkis et al. 2002) hereditary disease (Dyck et al, 1985) Dutsch et al, 2003), amyloid, alcohol abuse (Zambelis et al, 2005) or toxins (Kuo et al, 2005). Some sensory neuropathies that affect both the small and large nerve fibers can cause a reduction in epidermal nerve fiber density, before electrodiagnostic abnormalities.
How is SFN diagnosed
The diagnosis of small fiber neuropathy can be made with certainty, by demonstrating a reduction in the density of small nerve fibers in the skin. EMG and nerve conduction studies are usually normal in this condition, as they mostly measure the large nerve fibers in the motor or sensory nerves. The epidermal nerve fiber is normal in patients with central nervous system disease. (Latov; Brannagan)
For information on the diagnoising small fiber neuropathy through a skin biopsy click here.