What potential cause exists for a build-up of slowing minutes after hyperventilation is completed?

A build-up of slowing minutes after hyperventilation could indeed be associated with Moyamoya disease, which is a progressive cerebrovascular disorder characterized by stenosis (narrowing) of the arteries at the base of the brain. Following hyperventilation, which can increase cerebral blood flow and potentially exacerbate compromised areas of the brain, the slowing is indicative of ischemic changes or insufficient blood flow to affected regions. In the context of Moyamoya disease, the ability of the brain to adequately compensate for changes in blood flow dynamics is impaired, leading to changes in the EEG, such as increased slowing.

In cases involving multiple sclerosis, tumors, or previous strokes, the effects on the EEG after hyperventilation would typically differ and may not directly correlate to the classical presentation seen in Moyamoya disease. In multiple sclerosis, for instance, one might expect different patterns related to demyelination rather than a typical post-hyperventilation slowing. Similarly, tumor presence could lead to focal slowing rather than a widespread build-up. Previous strokes might produce chronic changes but would not specifically exhibit this response following hyperventilation in the same manner as Moyamoya disease.