Diagnosis of medical illness often starts with a thorough history then a physical examination to suggest possible diagnoses. This is often followed by testing to help sort through the possibilities. No test is 100% accurate, but test results can provide independent objective evidence about whether a particular diagnosis is or is not true.
Three tests are recommended by the American Academy of Neurology or the European Academy of Neurology: skin biopsy, autonomic function testing, and nerve biopsy.
A tiny skin sample is removed from a specific spot on the lower leg using local anesthesia. This is quite safe and does not require stitches. A biopsy can be removed in a doctor’s office anywhere and mailed to one of the special pathology laboratories that can process and examine it. For more information on skin biopsy, see Get Tested: Skin Biopsy. For listings of doctors who perform skin biopsies for diagnosing peripheral neuropathy around the world click here. Alternatively, most hospitals that analyze these biopsies also have someone who performs them. To arrange to have a skin biopsy performed at Massachusetts General Hospital, click here. Once a biopsy arrives at the laboratory, tiny sections of it are exposed to chemicals that make the nerve fibers within them visible (immunohistochemistry), and the number of nerve fibers in the surface layer (epidermis) is counted and compared to expected normal values. If the number of nerve fibers is very reduced from normal, this is accepted evidence that the patient has SFPN.
Electromyography (EMG) and Nerve Conduction Studies
These are electrodiagnostic tests that detect diseases that affect the nerves and muscles. EMG measures electrical activity in muscles, comparing electrical signals from muscles when they are at rest with when they are active. Nerve conduction studies measure how fast nerves can conduct electrical signals and how well they are conducted. Click here for more information about EMG and nerve conduction studies.
Autonomic Function Testing (AFT)
This series of tests measures autonomic functions (blood pressure, heart rate, and ability to sweat) during various activities. Four specific tests are performed:
- Recording sweat response from four electrodes placed on the skin of the arm, leg and foot.
- Recording heart rate and blood pressure during deep breathing.
- Recording heart rate and blood pressure while blowing into a tube.
- Recording heart rate and blood pressure while lying horizontal for five minutes, then in a standing position for 10 minutes, then lying horizontal again for five minutes.
This is an older technique performed only at special centers including Massachusetts General Hospital. A surgeon remove a small piece of a sensory nerve under anesthesia, usually from the lower leg, and send it for pathological study. For many but not all patients, skin biopsy can replace nerve biopsy. Nerve biopsies remain useful for detecting inflammatory causes of neuropathies such vasculitis and sarcoidosis, and for diagnosing nerve tumors or infections such as leprosy.
Ultrasound imaging allows physicians to directly view nerve damage. Different diseases affect nerves in characteristic ways, some of which can be seen with ultrasound. Ultrasound is well suited for detecting nerve entrapments, such as carpal tunnel syndrome. It is also proving useful for diagnosis and follow-up of inflammatory neuropathies. Click here for more information about nerve ultrasound.
If you have been diagnosed with polyneuropathy, your clinician may order blood and other tests to identify its underlying medical cause. Many such causes can be treated, offering the possibility for improvement of the neuropathy and its symptoms.
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