Abstracts

Rationale: We report unique EEG changes in a patient with MMD, referred for investigation of possible seizure, ultimately found to be experiencing reversible cerebral hypoperfusion. To our knowledge, this is the first report on EEG findings associated with clearly defined reversible cerebral hypoperfusion due to decreased autoregulatory capacity. Methods: A 20 yr old woman presented with an episode of loss of consciousness, followed by new dysarthria persisting for 4 months. She had suffered bilateral fronto-parietal strokes at 1 yr. Seizures had been present in early childhood, remitting by age 10, when MMD was treated with revascularization surgery (bilateral EDAS). She was subsequently stable on Aspirin 180 mg OD. An EEG demonstrated normal background with frequent medium-high amplitude slow sharp waves recorded with bilateral synchrony over the temporo-parieto-occipital watershed regions, in slow periodic trains (0.5-0.75 Hz), the slow sharp waves showed maximal amplitude at P3>T5>O1 (with a similar distribution on the right side, of slightly lower amplitude). The trains of slow periodic discharges at times lasted > 20 seconds, without clinical correlate. An MRI showed no new ischemic lesions. Conventional angiography showed abnormally dilated vessels, moyamoya collateral vessels and stenoses of the supraclinoid ICAs bilaterally. CVR study showed severe bilateral reduction in vascular reserve compared to 3 years earlier; specifically, paradoxical reactivity (steal) in the left MCA and PCA territories, with corresponding, less severe, right hemispheric watershed loss of reserve. The distribution of maximal CVR loss co-localized with the left-sided amplitude predominance of the PLED-like watershed region EEG discharges. Given the high risk of recurrent ischemic events with impaired CVR, an omental transplant was performed to improve cerebral hemodynamics in the left hemisphere. Three months post-op bilateral hemispheric improvement in CVR correlated with resolution of the periodic slow sharp waves seen on the initial EEG. Results: In MMD cerebral autoregulation maintains normal cerebral blood flow despite reductions in cerebral perfusion pressure (CPP) through vasodilation of resistance vessels downstream of stenotic lesions. This vasodilatory capacity is finite: reduction in CPP beyond a certain limit will lead to maximal dilation of resistance vessels and exhaustion of CVR. This patient's EEG showed a slow PLED-like pattern with maximal amplitude correlating with impaired CVR between the MCA and PCA watershed territories. Conclusions: The patient's presentation with suspected seizure may represent syncope due to cerebral hypoperfusion or an ictal epileptic phenomenon arising from the slow periodic PLED-like pattern. Revascularization improved CVR and clearly led to resolution of the EEG pattern, demonstrating a distinct association between the slow PLED-like phenomenon and reversible ischemia. This may have important diagnostic and therapeutic implications: the EEG changes may point to salvageable brain tissue experiencing compromised blood flow.