Answer
SSEP studies are the most widely used EP tests. Stimulation occurs at the extremity, and recordings are made on the scalp, near the sensory cortex. This technique may be used to locate the level of the injury in the nerve root, spinal cord, or brain. In CNS insults, such as spinal cord trauma and stroke, SSEP testing has been helpful in establishing the degree of insult and in determining its prognosis.
SSEPs can also be used to localize demyelinating diseases, such as multiple sclerosis, and root level injuries in cervical and lumbar radiculopathies. [23]
A retrospective study by Devic et al indicated that SSEPs can aid in the diagnosis of chronic inflammatory demyelinating polyneuropathy (CIDP) when nerve conduction studies (NCSs) fail to reveal peripheral demyelination in patients with other signs of the disease. The study involved 26 patients with clinical signs of CIDP, with SSEPs in 22 of the patients (85%) demonstrating abnormal proximal conduction in sensory fibers; this included 16 of 20 patients (80%) who responded to immunotherapy, considered to be confirmation of CIDP. [24]
In addition, SSEPs can be used to determine the level of coma and to evaluate for brain death. [25] SSEPs are also useful for intraoperative monitoring of patients undergoing neurosurgical procedures.
In 2018, the International Society of Intraoperative Neurophysiology published recommendations regarding the intraoperative monitoring of SSEPs. These included the recommendation that propofol and opioid total intravenous anesthesia be used during surgery to avoid the dose-dependent suppression of polysynaptic cortical SSEPs found with inhalation anesthetics such as nitrous oxide and to facilitate a higher signal-to-noise ratio. The recommendations also specified the use of an adaptive warning criterion consisting of “visually obvious amplitude reduction from recent pre-change values” that clearly exceeds variability, “particularly when abrupt and focal.” [26]
-
Sensory nerve action potential.
-
Motor nerve action potential.
