EMG/Nerve Conduction studies. Electromyography (EMG) and nerve conduction studies assess the integrity and function of muscle and nerve, respectively. The EMG test allows the neurologist to distinguish neuropathic from myopathic disease and define the precise distribution of muscle involvement. Nerve conduction studies inform the neurologist about the integrity of sensory or motor nerves; an electrical stimulation is applied to the skin overlying a peripheral nerve to enable a recording of the speed of conduction and amplitude of the “downstream” action potential. NCS assist in the diagnosis of nerve disorders, such as demyelinating neuropathy (slow conduction velocity), axonal neuropathy (reduced amplitude of CMAP), and root compressions.
Skin Biopsy. Lyme disease can cause a neuropathy with associated sensory symptoms and sensory loss. To detect small-fiber damage, skin biopsies are now being performed in many diseases that cause neuropathies. In diabetes, some studies suggest that the density of intraepidermal nerve fibers (IENF) is correlated with the extent of the neuropathy and with the duration of disease; lower density correlates with higher neuropathy scores In other systemic diseases, such as Lupus, sarcoid, sjogren’s, celiac, and hypothyroidism, skin biopsy has been used to show a correlation between small-fiber degeneration and neuropathic symptoms. IENF density is a general marker of axonal integrity in peripheral neuropathies, but it cannot be used to make a specific diagnosis. Recently, neurologists have begun to examine patients with Lyme disease to assess small nerve fiber density. The skin biopsy procedure itself is typically performed with a 3-mm disposable circular punch needle with a sterile technique using local anesthesia (2% lidocaine and epinephrine).
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