Clinical neurophysiology

Abstract

The electroencephalogram (EEG) is a simple, non-invasive test of brain function that is mostly used for the diagnosis and classification of epilepsy. Bilateral 3/second spike and slow wave complexes are seen in primary generalized epilepsy and localized spike discharges occur in partial seizures. Prolonged recordings of seizures, allowing a clinical and electrographic correlation, are helpful for precise diagnosis. The EEG may show characteristic waveforms (slow waves, triphasic or repetitive complexes) that help in the management of other brain diseases such as encephalitis and encephalopathy. Evoked potentials are used to confirm the presence of central nervous system demyelination in suspected multiple sclerosis where imaging changes are equivocal. Operative or intensive care unit monitoring of central nervous system function with evoked potentials or EEG are used in spinal surgery and for patients with status epilepticus or head injury. Nerve conduction and needle electromyography (EMG) are used to investigate peripheral neuromuscular disorders, especially to confirm the presence and assess the severity of peripheral nerve disease. Clinical neurophysiologists are often asked to investigate patients with undiagnosed neurological symptoms, and in these patients the tests provide objective information as an extension to the clinical examination. Measurement of sensory nerve action potentials helps locate lesions in sensory pathways. A combination of motor nerve conduction and needle EMG is particularly useful when investigating patients with weakness. Specialized computer-based EMG studies help quantify abnormalities in myasthenia, motor neurone diseases and primary myopathy.