EMG or Electro-Myo-Graphy
- EMG or Electro-Myo-Graphy isa test where a electrical needle is placed in a muscle to record its electrical activity. It is used
to differentiate other causes of muscle weakness, such as myopathy (inflammation of muscle), axonal neuropathies (Dysfunction in the center of the nerve) and
disorders of neuromuscular transmission (dysfunction at the place where a nerve connects to a muscle) seen in Myasthenia. Its Not a diagnostic Test
meaning the EMG cannot tell you what is the diagnosis. For complete details we will send you to a in detail EMG page to learn
NCV is a Nerve-conduction-Velocity is the second part of the Electrophysiological Test. In NCV a nerve is shocked by a electrical currentand the time this current takes to reach a second point is measured. If the speed of this measured electrical conduction is slow, then the nerve conduction studies show demyelination or CIDP. If the speed is slightly slow then a axonal neuropathy is considered which may be due to vitamin deficiency. Axonal or Demyelinating both forms respond to anti-inflammatory treatment. Its Not a diagnostic Test Meaning the test cannot give you a diagnosis. The test can just tell you weather the nerves conduct electricity at slow of fast speeds and in most cases of cidp this test will be normal as most cidp is due to small fiber neuropathy and the small fiber speeds cannot be checked by NCV.
Some of the NCV findings include: (see this link for EMG findings in CIDP)
(a) a slowing in the nerve conduction velocities ;
(b) the presence of conduction block(meaning no or little electrical current is transmitted in the nerve). Is seen in Mutli Focal Motor Neuropathy.
(c) prolonged distal latencies in at least two nerves; (means that it takes a long time for the current to get past the ends of the nerve)
(In some case EMG/NCV can be normal). EMG does not tell what is the cause of your disease, it can only locate the site of the damage.
- CSF Examination:Cerebro Spinal Fuid is the fluid that bathes your brain and spinal cord. Cytoalbuminologic dissociation (means elevated CSF protein >45 in the absence of a high cell count <10) is characteristic of CIDP & GBS. CSF pleocytosis (excess of white cells) is rare except in HIV-associated CIDP.
Not all the patients will have lab abnormalities. In many the EMG/NCV findings will not show that they have CIDP yet they will still have the disease.
Is EMG/NCV Insensitive in the Diagnosis of CIDP?.
The clinical profile of chronic inflammatory demyelinating polyneuropathy(CIDP) is variable.The current EMG criteriafor CIDP is not sensitive.EMG IS INSENSTIVE & non diagnostic test.
In a study electrophysiologic abnormalities were those of simple axonopathy in 7 patients; the other patient had almost normal electrophysiologic results. The, examination of nerve biopsies in all 8 patients revealed loss of myelinated fibers; and various degrees of onion bulbs. These histology findings were identical to those of the 36 other CIDP patients. The authors conclude that many patients with unrecognized CIDP are erroneously classified by electrodiagnosis as having chronic axonal neuropathy and that nerve biopsy should be considered to further investigate a chronic idiopathic neuropathy.
Click to view different size nerve fibers.
Neurology. 2002 Dec 24;59(12 Suppl 6):S2-6.
Diagnosis of CIDP. Latov N. Peripheral Neuropathy Center, Weill Medical College of Cornell University, New York, NY 10022, USA.
..patients with neuropathy ofunknown etiology are more likely to have CIDP than idiopathic axonal neuropathy, and warrant a trial of therapy . A favorable response to therapy, consisting of stabilization or improvement of the neuropathy, would confirm the diagnosis