Neuro-electric responses to sensory stimuli can be readily and non-invasively recorded using averaging techniques first employed by Dawson in 1947.¹ The evoked responses can be quantified by measuring peak amplitudes and latencies, in the millisecond (ms) domain, and they provide numerical data that are quantitative extensions of the neurological examination. The clinical utility of evoked potentials (EPs) is based on their ability to:

• demonstrate abnormal sensory system conduction, when the history and/or neurological examination is equivocal

• reveal subclinical involvement of a sensory system (“silent” lesions), particularly when demyelination is suggested by symptoms and/or signs in another area of the central nervous system

• help define the anatomic distribution and give some insight into pathophysiology of a disease process

• monitor changes in a patient’s neurological status.

In theory almost any sensory modality may be tested, although in routine clinical practice pattern reversal visual evoked potentials (VEPs), short latency somatosensory evoked potentials (SSEPs), and brainstem auditory evoked potentials (BSAEPs) are tested most frequently. Longer latency responses that are related to higher “cognitive” functions such as event related potentials (ERPs), contingent negative variant (CNV), and sensory potentials after stimulation with CO₂ lasers are not routinely used in clinical practice and are beyond the scope of this article.

EPs have the advantages of being objective, often more sensitive than detailed neurological examination, and they can be recorded in patients who are anaesthetised or comatose. The latter fact, along with improvements in recording equipment, has led to newer applications in the operating theatre and intensive care unit (ICU)—at a time when the role of EPs in the assessment of multiple sclerosis has largely been replaced by magnetic resonance imaging (MRI). A recent evidence based review recommended that VEPs are probably useful and SSEPs are possibly useful in identifying patients who are at increased risk …