SSEP
A somatosensory evoked potential (SSEP) is an evoked potential caused by a physical stimulus (usually a small electric pulse). Electrodes positioned over particular areas of the body record responses of the SSEP, these are then observed as a reading on an electroencephalogram (EEG). A SSEP can most commonly involve stimulation of the median nerve at the wrist, or the posterior tibial nerve at the ankle. This investigation therefore tests the pathway of the sensory nerves to the sensory areas of the brain, even though the stimuli are non-physiological.
When is the SSEP used?
A doctor may recommend you go for a SSEP test if you have been experiencing feelings of numbness or weakness in your arms or legs that may be due to problems affecting the somatosensory nerve pathway. These feelings are often very subtle and not easily detected in a routine clinical examination.
What does the SSEP detect?
- 1) From the SSEP, a neurologist is able to determine the time it takes for nerve fibres to relay a stimulus from the point of stimulation (wrist or ankle) to a detection site on the scalp, neck or back. By analysing the SSEP pattern, the neurologist can get an idea of how well these sensory nerves are working. Multiple sclerosis (MS) for example, can damage the myelin sheath insulating nerve fibres of the brain and spinal cord in a process called demyelination. The damage means it takes a longer time for signals to be relayed along nerve pathways, or they may be blocked, resulting in changes in the SSEP.
