Porphyria Educational Services
PORPHYRIA EDUCATIONAL SERVICES BULLETIN Vol.1 No. 15 April 11, 1999
FOCUS: Diagnosis of Peripheral Neuropathy in Porphyria
THE EMG and PN
For determing Peripheral Neuropathy [PN] a testing by a neurologist must be done.
First there is the simple pin sticking checking for nerve impulse.
Then the rubber tipped hammer to check for tendon reflexes.
Then the biggie... an EMG [Electromyography].
Electromyography is a diagnostic neurolic test to study the potential [electrically measured activity] of muscle at rest, the reaction to contraction, and the response of muscle to insertion of a needle. The test is an aid in ascertaining whether a patient's illness is directly affecting the spinal cord, muscles or peripheral nerves.
How is the test performed?
The patient lies at rest while the peripheral nerves in various are stimulated through electrodes, and the electrical activity in the muscle at rest, on insertion of the needle, and during the muscle contraction. The test is sometimes employed as a measure of the muscle tension produced by nercous stress, usually, the muscles of the forehead are tested, since they can indicate relaxation of generalized body tension.
Electromyoneurogra[hy is the combined use of electromyography and neurography. The two tests offer a more precise means of finding the exact location of nerve damage or disorder.
Dynomometry testing uses a dynomometer [most often a dial guage attached to a spring mechanism that measures the strength of muscles] to ascertain certain physical abilities such as holding an object in the hand. It helps detect diseases of the nerves from the spinal cord to the muscle.
There is negligible risk factor in running this test. All that is involved is the catheter and needle insertion along with the elctrical instruments.
The pain and discomfort from the test focuses on the needle insertion, which is usually done without local anesthesia. This can be quite uncomfortable and at times even very painful.
Intrepretation of the tests must be made by a neurologist. In the normal values, when the muscle is at rest, no electrical activity is observed. When the muscles contract, the elctromyograph will show a smooth graphic wavelike respresentation of ech contraction. The graph lines are amplified with the increase in strength of each contraction.
When the values are abnormal,muscle disease will produce a spiked wave pattern. The shape of the spike depends on the particular disease.
Muscle weakness produces a diminished wave. With myasthenia gravis, for instance, the waves disappear for a few minutes. Nerve involvement, as aooposed to muscle involvement, usually shows a decreased frequency of contractions.
Current costs of this test runs from$150 to $350 depending on how many muscles or nerves are tested. If all of the extremities are tested, the fee can run to $650. Also, when elctromyoneurolography is used the total cost can run to around $500.
Neurologist consider the test quite reliable and rate it as 90 percent accurate.
As stated by a nurologist, "it is quite quite difficult for a pretender /malingerer to fake to have muscle pathology when muscles respond to electric stimulation.