Nerve conduction study (NCS) or nerve conduction velocity (NCV) test tests the speed of nerve impulse through a nerve. NCV tests the extent and severity of nerve injury. During the NCV test, the nerve is stimulated with a stimulator, and electrical impulses of nerves are assessed by two electrode patches applied on the hand or leg. This procedure is repeated for every nerve to be tested.
In The NCV test, the nerve conduction velocity (speed) is then calculated by measuring the distance (in mm) between electrodes and the time taken for nerve impulses to travel
EMG test may sometimes be done after NCV test. An EMG test assesses the electrical activity in muscles.
Both NCV and EMG tests are used to assess the presence, location, and extent of damage to the nerves and muscles.
NCV test takes around 30-60 min and EMG test takes 30-45 min.
No special precautions are there for the NCV and EMG test
You will have to bring all the previous NCV test and EMG records, MRI scans, X ray and CT scan and other related medical record before the test is done.
The NCV is performed by a trained technician or neurologist,
The procedure of NCV test and EMG test is as follows:
- You will be asked to wear a gown; remove jewellery, eyeglasses, hearing aids, or other metal objects as they might cause interference with the NCV test. Do not apply any moisturiser, lotion, creams, gels, oil on hands and legs for 2 days before the NCV test. Wash your hands and legs before the NCV test with soap water
- Kindly inform if you a cardiac pacemaker
- Test is better done in lying down position
- Commonly, 4-8 nerves are tested in upper limb and 3-5 nerves in lower limbs
- A recording electrode is attached to the skin with a special conducting paste and a another stimulating electrode is placed at 3-10 cm
- The nerve is stimulated by a low degree intensity electrical current shock given through the stimulator
- There might be minor discomfort for a few seconds.
- The stimulation of the nerve by electrical impulse will create a nerve impulse
- After the test, the patient can go walk and go home immediately
- Difficulty in standing or weakness in nerve and muscle disorders like Guillain-Barré syndrome
- Numbness of first three fingers of hands as in carpal tunnel syndrome. This happens more during night
- Pain, weakness, tingling or numbness in shoulder and arm due to cervical radiculopathy or cervical spine disease or slip disc in neck
- Back pain and pain in leg due to Herniated disc disease, slip disc, sciatica, PIVD, prolapse intervertebral disc. Pain is often more on one side of leg
- Peripheral nerve injury- due to accident, fracture
- Foot drop- injury in leg
- Wrist drop- injury to elbow
- Arm weakness due to brachial plexus injury, erb’s palsy
- Hand and wrist weakness due to fracture, surgery
- Difficulty in walking, weakness due to weakness, muscle disorders, dermatomyositis, polymyositis, inflammatory myopathy, muscle dystrophy, DMD, Duchene muscular dystrophy. This causes difficulty in getting up from bed and standing, climbing stairs
Tingling and numbness, pain in nerves, burning sensation in nerves In Diabetic neuropathy, multiple sclerosis, CIDP, chronic inflammatory demyelinating neuropathy, b12 deficiency,
- The nerves have a lot of reserve. SO yes, in early cases NCV test can be normal even if there are severe symptoms. In such cases, comparison with other limb helps in making a diagnosis. As a rule, NCV test is done in both hands and both legs. In diabetes, NCV test of all 4 limbs is suggested
- Autonomic neuropathy due to diabetes and B12 deficiency can have normal NCV test early in the course of disease. Special tests like SSR test can be done in diabetes patients.
- Many patients with back pain, prolapse disc, slip disc can have normal NCV test in early stage of disease even with a grossly abnormal MRI. Serial NCV are better indicators to assess worsening rather than one time NCV
- On the contrary, dipropionate abnormality in NCV with normal MRI are typically seen in neuropathic disorders
- NCV test will be normal in weak patients whose abnormality in nerves of brain
- Normal NCV may be seen in muscle disorders too in which diagnosis is made by detailed history, CPK NAC blood test and EMG test.
Typically NCV test is done in both lower limbs (legs) or both upper limbs (hands) if the symptoms are in legs and arm respectively. This is because, the results of NCV test are compared with opposite limb
In diabetic patients, cancer patients, rheumatological disorders, SLE, RA, rheumatoid arthritis, and alcoholics the NCV test is recommended to be done in all 4 limbs
Nerve disorder is also called as neuropathy. Usually, MRI test is also ordered in cases of neuropathy. Other blood test like CBC, hemogram, ESR, B12, ANA IFA, Ra factor, lipid profile, HBA1c are other tests which need to done in case of nerve disease. These test are individualised depending on age