What is Clinical Neurophysiology?
The clinical neurophysiologic examination is an extension
of a neurologic consultation, not just a set of laboratory tests. It does
not only verify or exclude a clinical suspicion but also gives precise definition
of site, type and degree of lesion and reveal abnormalities that are clinically
uncertain, silent or unsuspected.
In US and in many European countries the EMG and EEG laboratories often are
linked to neurology or physical medicine and rehabilitation and the laboratories
are run by doctors with clinical responsibilities. However, in the Scandinavian
countries and Great Britain, the departments of clinical neurophysiology are
usually independent laboratores run by specialists in CN. This separation
from patient care has the advantage of allowing high degree of specialisation
and specific research in the field. It may have the disadvantage that the
clinical neurophysiologist looses the clinical feedback. In many places this
has been compensated by frequent rounds with referring clinicians. In Sweden
CN is an independent specialty since late 50ties. It is established at each
university and only the specialits in these institutions are performing EMG,
EEG, evoked potentials and neuro-monitoring. Training for the specialty includes
4 years in clinical neurophysiology and 0.5 year in neurology. A similar training
is available in Norway, Finland, Denmark and Great Britain.
In general, the neurophysiologic methods describe and quantify functions
and pathophysiologic changes in central and peripheral nervous system. They
reflect, but do not measure directly biochemical or morphologic aspects of
central or peripheral nervous system. This distinction to other methods and
measurements should be made clear. Adequate techniques should be applied for
each specific question.
Within neurophysiology there is continous development of new sophisticated
methods for understanding of pathophysiologic mechanisms. EMG (electromyography)
describes functional status of central and peripheral nervous systems and
is complementary to other techniques for evaluation of the neurologic patient.
Various categories of morphologic and physiologic changes are seen in the
motor unit in most nerve-muscle disorders. They are either acute, often functional
in nature or slowly developing with morphologic correlates. These changes
provide help in the assessment of a diagnosis or in testing the short term
effect of drugs and the latter may also be used to monitor changes in a disease
or response to therapy. The morphologic changes may be related to severity
of the disease or to repairative processes. Therefore, some of them are inversely
correlated to the clinical picture e.g. high degree of reinnervation may produce
a good compensation for functional defecit which then may be difficult to
The EEG method (electroencephalography) involves the recording of the
weak currents from the cerebral cortex with surface electrodes mounted on
the scalp of the patient, thus monitoring the functional status of the brain.
The main indication for the EEG investigation is the suspicion of epileptic
seizures, however, the method will show any dysfunction in the brain that
involves the signalprocessing in the neuronal network changing the electric
activity in the brain cortex. The transformation from analog recordings with
paper printers to digital recordings with the signal displayed on a screen
and data sampled on to a hard disc has given the possibilities of quantitativa
analysis of the brain activity. There are also new methods wich allows a source
localisation of electric activity in the brain (dipole analysis) which combined
with structural neuroimaging (MRI) gives quite new information on normal brain
function as well as pathology.