Neurophysiologic Services (Electro diagnosis)
» Evoked potentials (EP)
» Electroencephalography (EEG)
» Sleep studies (polysomnography)
Electro diagnostic studies can be helpful in evaluating weakness,
numbness, pain and symptoms such as fatigue, cramps and abnormal
sensation. Electro diagnostic evaluation is an extension of the
neurologist's physical examination and is performed by our clinical
neurophysiologist who is a neurologist with special training in
clinical neurophysiology. The time required to complete the study
generally takes approximately 60 to 120 minutes. The two main
procedures used to study nerves and muscles are needle
electromyography (EMG) and nerve conduction velocity studies (NCV).
During an EMG, the neurologist analyses the electric activity in
muscles by inserting a fine needle electrode into selected muscles.
Needle insertion may cause mild temporary discomfort. The needle is
not used for injection and no shocks are given. The physician can
determine whether the muscle is working normally by seeing the
electric activity on a screen and listening over a loudspeaker. The
needles are discarded after use or sterilized to prevent the
transmission of AIDS, hepatitis and other infections.
To perform nerve conduction studies, the physician tapes small metal
electrodes on the skin and applies a brief electric stimulus to one
portion of a nerve. Nerve stimulation will cause a tingling
sensation. The physician can then evaluate the electric response of
the nerve or muscle to which the nerve is attached and determine if
the nerve impulse is a) conducted normally, b) at a slow speed or c)
not transmitted at all, suggesting damage to the nerve.
Electro diagnosis may also include a number of other tests, such as
evoked potentials. These studies use different stimuli, such as
auditory clicks, a changing visual pattern such as a checkerboard,
or small electric stimuli applied to specific nerves. The recordings
are made over the surface of the head and the spine to evaluate
whether the sensory impulses are conducting normally through the
nerves, spinal cord or brain.
The patient does not need to do anything special to prepare for this
test, except to keep the skin free of any lotions or emollients on
the day of the examination. Be sure to inform the physician,
however, if you are taking blood-thinning medication such as
Coumadin, have hemophilia or a cardiac pacemaker. Patients with
myasthenia gravis should ask their physician whether or not to take
anti-cholinesterase medications on the day of the test.
EEG is the single most important laboratory test in the evaluation
of patients with seizures and related disorders. It is a painless
procedure, during which the brain's electrical activity detected by
electrodes pasted to the scalp is amplified and recorded. The test
lasts for approximately one hour. Patients are advised to keep their
hair free of any oil and grease and not to be fasting before the
test. They should also continue taking any medicines prescribed to
them. At Apollo Hospitals, advanced computerised Digital EEGs offer
off-line data analysis for greater diagnostic yield.