Proper diagnosis of peripheral nerve injuries can be challenging because identifying the extent of the injury is often difficult. The diagnosis techniques will vary from patient to patient, injury to injury, as well as physician to physician. One of the first steps in diagnosing a peripheral nerve injury is an examination by a qualified healthcare professional. During the examination the healthcare professional may administer a medical history questionnaire, test the patient’s muscle strength, reflexes, and/or their ability to detect subtle variations in sensation, pressure, temperature, and pain in the affected area.
If your doctor believes there is a possibility of nerve injury, he or she may use more specific tests to determine the extent of the injury. Examples of these techniques are:
2 Point Descrimination
A 2-point discrimination test measures a person’s ability to tell the difference between two points on the skin. This determines how sensitive the area is to touch and can identify if there is a sensory deficit. It is mainly used in highly innervated areas such as the lips and fingertips and is a quick, noninvasive way to test for nerve dysfunction.
A Semmes-Weinstein monofilament test is used to measure loss of sensation. Different sized monofilaments are placed on the skin and force is added to bend the filament. When there is nerve damage, a patient may not be able to detect certain filaments. Monofilament testing is a quick, noninvasive way to test for nerve damage.
Doctors may test the area using heat (warm instrument), cold (ice cube), and pain (needle prick). A person with normal nerve sensation should be able to feel all of these stimuli. A lack of response to any one of these could mean there is a nerve injury.
Both Magnetic Resonance Imaging (MRI) and Computer Tomography (CT) are examinations that provide a detailed view of the area in the body where the nerve damage is suspected. The image produced by these examinations can be used by the doctor to investigate any possible structural damages to the nerves, including scarring from an injury, nerve tumors, or pressure from a surrounding structure.
Nerve Conduction Velocity (NCV) measures how well electrical signals are conducted through the nerves. The examination uses two electrodes, a stimulating electrode placed above the injury, and a recording electrode placed below the injury. The nerve is stimulated by passing an electrical signal through the stimulating electrode, and time is kept until the stimulating electrical signal is measured by the recording electrode. The distance between the two electrodes is divided by the measured time to produce the nerve conduction velocity. A decrease in nerve conduction velocity may be a sign of damage to the nerve.
An Electromyogram (EMG) examination can be used to determine how well a motor nerve is working by measuring the electrical activity present in a muscle. The examination works by placing a sensing electrode into the muscle and measuring the difference in electrical activity between when the muscle is at rest and when the muscle is contracting. Impaired EMG readings may be a sign of damage to the nerve.