CRPS Nerve Damage
Although CRPS may not be caused by direct damage to a nerve, the patient’s nerves in the affected area typically play a significant role in the condition. Therefore, nerve testing can be a large contributor to diagnosing CRPS and evaluating the efficacy of treatment. CRPS nerve testing can help to identify certain types of nerve damage in the affected area. The type, nature, and severity of nerve damage can help to indicate a CRPS diagnosis as opposed to other conditions which may cause similar symptoms.
Type I vs. Type II CRPS
Nerve testing can be especially helpful in determining type I versus type II CRPS. Type I CRPS is generally classified as CRPS where there is no observable nerve damage. Type II CRPS is characterized by specific damage to a nerve, which typically occurred during a traumatic event such as an injury or surgery. Nerve testing that reveals damage to the tested nerve may indicate Type II CRPS.
Nerve Conduction Velocity
Nerve conduction velocity (NCV) tests the speed of electrical signals through certain nerves in the peripheral nervous system. During a nerve conduction velocity test, the nerve is stimulated using an electrical impulse. Specialists then observe the speed at which the electrical impulse courses down the nerve. In most cases, decreased nerve conduction indicates disease or abnormalities within the nerve.
Nerve conduction velocity may also be used for conditions such as:
- Carpal tunnel syndrome, a condition affecting the median nerve in the forearm
- Diphtheria, an upper respiratory bacterial infection that may lead to nerve damage
- Diabetic neuropathy, or nerve damage as a result of diabetes
- Brachial plexopathy, or nerve problems in the arm and shoulder region
- General paresis, a condition causing brain nerve damage due to untreated syphilis
Nerve Conduction Velocity Procedure
Nerve conduction velocity is typically performed using surface patch electrodes. Surface patch electrodes are placed on the skin located above the nerve that doctors wish to examine. One of the electrodes emits mild electrical impulses, which travel through the skin directly to the nerve. The electrical activity that results is then recorded by additional electrodes. The speed of the impulses, or nerve conduction velocity, is measured using a mathematical formula involving the distance between the electrodes and the time it takes for the electrical impulses to travel from one electrode to another.
An electromyogram (EMG) is a type of nerve testing that may be performed in conjunction with nerve conduction velocity. An electromyogram also measures electrical activity. However, electromyograms measure activity within muscles as opposed to nerves. This can be helpful, as muscle abnormalities can often indicate nerve damage related to CRPS.
During an intramuscular electromyogram, a needle is inserted through the patient’s skin and into the muscle. This needle serves as an electrode by detecting and recording electrical activity. Depending on the size of the muscle being observed, several needles may be needed to perform a thorough electromyogram. After the needle electrodes are inserted, the doctor may ask the patient to contract the tested muscle. If a leg is being tested, the patient may be asked to bend the leg.
Quantitative Sensory Testing
Quantitative sensory testing (QST) is used to assess damage in small and large nerve endings. Small nerve endings detect temperature changes, while large nerve endings detect vibration. Quantitative sensory testing will typically allow doctors to observe location and severity of nerve damage. During QST, tested nerves will be subjected to vibration and changes in temperature. This type of nerve testing may also be used to evaluate whether or not a patient with CRPS or another type of neuropathy is responding positively to current treatment.
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Uluc, Kayihan, et al. “Near-Nerve Needle Sensory and Medial Plantar Nerve Conduction Studies in Patients with Small-Fiber Sensory Neuropathy.” European Journal of Neurology: The Official Journal of the European Federation of Neurological Societies 15.9 (2008): 928-932. MEDLINE with Full Text. Web. 2 Mar. 2014.