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Editors Selection IGR 8-3

Bloodflow

Comment by Selim Orgül on:

13419 Comparative study of cerebral blood flow in patients with normal-tension glaucoma and control subjects, Sugiyama T; Utsunomiya K; Ota H et al., American Journal of Ophthalmology, 2006; 141: 394-396

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Structural neuroimaging has an important role in initial evaluation of dementia for ruling out potentially treatable causes and especially distinguishing patients with frontotemporal dementia from those with Alzheimer disease. There is also increasing recognition of a class of elderly people with complaints of memory loss but who do not meet the criteria for dementia. This disorder, called 'mild cognitive impairment' often converts to Alzheimer disease. Neuroimaging is sensitive to structural and functional changes in the brains of patients with mild cognitive impairment and valuable in predicting future development of Alzheimer disease in these patients. Indeed, the rate of hippocampal volume loss on magnetic resonance imaging correlates with clinical disease progression in the cognitive continuum from normal aging to mild cognitive impairment and to Alzheimer disease. Furthermore, cerebral blood flow on SPECT is associated with the rate of cognitive decline in patients with Alzheimer disease. Especially reduced blood flow in temporal parietal association areas is associated with a higher risk of progressive cognitive decline in patients with mild cognitive impairment.

Altered cerebral blood flow has also been demonstrated in glaucoma patients. Using transcranial Doppler, reduced blood flow velocities have been demonstrated in primary open angle glaucoma patients. Additionally, hyperoxia known to decrease blood flow velocities in the mean cerebral artery did not cause significant changes in open angle glaucoma patients in a relatively recent clinical study. Furthermore, cerebral autoregulation seams to be impaired in open angle glaucoma patients, allowing transmission of oscillations of the mean arterial pressure onto cerebral blood flow, which has been hypothesised to possible increase the risk of cerebral vascular disorders in glaucoma patients. Finally, a hypothesis that cumulative effects of exposure to high intracranial pressure may contribute to the development of Alzheimer's disease has been formulated already over a decade ago. Based on this background, Sugiyama et al. (123) have evaluated regional cerebral blood flow in normal tension glaucoma patients using Iodine-123-N-isopropyl-P-iodoamphetamine single photon emission computer tomography (SPECT).

Described in a short report, the provided details are scarces and the results of this study are not easy to interpret. The patients were recruited, without obviously being tested regarding their cognitive functions. The authors classified the neuroimaging results into three categories. The finding of a decrease in blood flow from the parietotemporal to the temporal lobe was classified as Alzheimer disease like pattern. In a subgroup of the recruited patients, they could evaluate progression of visual field damage, obviously on a retrospective bases. Seven out of 31 cases displayed what the authors call an Alzheimer disease like perfusion pattern, and among the patients evaluated with regard to visual field progression, 80% of those with Alzheimer disease like pattern cerebral blood flow showed visual field deterioration while this was only the case for 63% or less of the patients in the other two groups. This difference was statistically not significant and the authors compared the quantitative regional cerebral blood flow data between controls and the normal tension glaucoma group in 22 different cerebral regions. In three regions they noted a statistically significant result, which, however, given the large number of comparisons, is not easy to interpret. Nevertheless, this pilot study points to a possible parallelism between a neurodegenerative disease of the brain and of the eye, possibly linked by altered blood flow. The hypothesis is appealing but will have to await further confirmation.

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