CHANGES IN LOCAL CEREBRAL BLOOD-FLOW BY NEUROACTIVATION AND VASOACTIVATION IN PATIENTS WITH IMPAIRED COGNITIVE FUNCTION

Imaging of local cerebral blood flow (lCBF) may serve as an important supplementary tool in the aetiological assessment of dementias. In ear ly or preclinical disease, however, there are less characteristic chan ges in lCBF. In the present study it was investigated whether vasoacti vation or neuroactivation may produce more pronounced local lCBF defic its. Local CBF was investigated by using technetium-99m hexamethylprop ylene amine oxime and single-photon emission tomography (SPET) in 80 p atients (50 with mild cognitive impairment and 30 with dementia of Alz heimer type (DAT), all without evidence of cerebrovascular disease) at rest (baseline) and during activation. In 31 studies patients underwe nt vasomotor activation with acetazolamide, while 62 studies were perf ormed under cognitive challenge (neuroactivation by labyrinth task). C ortical activity relative to that of cerebellum increased significantl y in a right temporal region and tended to increase in other cortical regions upon vasoactivation. In contrast, neuroactivation reduced cort ical activity relative to that of cerebellum in several left and right temporal and in left parietal regions. Visual classification of SPET images of patients with probable DAT by three observers resulted in a reduction of the number of definitely abnormal patterns from 9/12 to 4 /12 by vasoactivation and an increase from 10/18 to 15/18 by neuroacti vation. Correspondingly, abnormal ratings in patients with mild cognit ive dysfunction were reduced from 7/19 to 5/19 by vasoactivation and w ere increased from 12/21 to 18/21 by neuroactivation. In conclusion, v asoactivation does not enhance local relative perfusion deficits in pa tients with cognitive impairment of non-vascular aetiology, whereas ne uroactivation by labyrinth task produces more pronounced local flow di fferences and enhances abnormal patterns in lCBF imaging.