Polysomnographical assessment of the pathophysiology of West syndrome

In this brief review, the sleep studies on patients with West syndrome (WS) were summarized. In addition to the previously reported common finding for sleep in WS – reduction of the amount of rapid-eye-movement (REM) sleep – weakness of phasic suppression of chin muscle activity in WS patients has recently been found. The degree of this weakness is quantified by the phasic inhibition index (PII), which has been found to reflect a patientʹs prognosis as to convulsions. PII is proposed to be a useful parameter for assessing the prognosis of WS. Since the pontine tegmentum is involved in the production of the REM-related phasic loss of muscle activity in REM sleep, WS patients are hypothesized to have a functional instability of the pontine tegmentum. After adrenocorticotropin (ACTH) treatment, PII decreased significantly in all WS patients examined. Taken together with the effects of corticosteriods on PII, and the incidence of phasic chin muscle activity in patients with congenital adrenal hyperplasia and nephrotic syndrome, ACTH is hypothesized to suppress the spasms in WS patients not only through corticosteroids, but also through a direct action on the pontine tegmentum. Since PII has been reported to be elevated in patients with an autistic tendency, the appearance of an autistic tendency is also hypothesized to be involved in the functional disturbance of the pontine tegmentum.