Determination of cerebral blood flow by SPECT: a valuable tool in the investigation of dementia?

Retinal photography: A window into the cardiovascular-brain link in adolescent bipolar disorder

OBJECTIVE

The burden of cardiovascular disease in bipolar disorder (BD) exceeds what can be explained by traditional cardiovascular risk factors (CVRFs), lifestyle, and/or medications. Moreover, neurocognitive deficits are a core feature of BD, and are also related to CVRFs. We examined retinal vascular photography, a proxy for cerebral microvasculature, in relation to CVRFs, peripheral microvascular function, and neurocognition among BD adolescents.

METHODS

Subjects were 30 adolescents with BD and 32 healthy controls (HC). Retinal photography was conducted using a Topcon TRC 50 DX, Type IA camera, following pupil dilation. Retinal arteriolar and venular caliber was measured, from which the arterio-venular ratio (AVR) was computed. All measures were conducted masked to participant diagnosis. Peripheral arterial tonometry measured endothelial function. Neurocognition was assessed using the Cambridge Neuropsychological Tests Automated Battery.

RESULTS

AVR was not significantly different between groups (Cohen's d=0.18, p=0.103). Higher diastolic blood pressure (BP) was associated with lower (worse) AVR in BD (r=-0.441, p=0.015) but not HC (r=-0.192, p=0.293). Similarly, in the BD group only, higher (better) endothelial function was associated with higher AVR (r=0.375, p=0.041). Hierarchical regression models confirmed that, independent of covariates, retinal vascular caliber was significantly associated with diastolic BP and endothelial function in BD. Within the BD group, mood scores were significantly negatively correlated with AVR (β=-0.451, p=0.044).

LIMITATIONS

This study's limitations include a small sample size, a cross-sectional study design, and a heterogeneous sample.

CONCLUSION

Retinal photography may offer unique insights regarding the cardiovascular and neurocognitive burden of BD. Larger longitudinal studies are warranted.

Hypertensive retinopathy: there's more than meets the eye

Hypertension is associated with increased cardiovascular risk, leading to systemic end-organ damage, including retinopathy. However, the recent European Society of Hypertension-European Society of Cardiology and World Health Organization-International Society of Hypertension 2003 guidelines propose new prognostic indications for the classification of hypertensive retinopathy. In particular, grades I and II are no longer included among signs of end-organ damage, and only grades III and IV are retained as associated clinical conditions for the stratification of global cardiovascular risk. This review article will focus on the wider implications of clinical markers of microvascular damage in the retina, with specific reference to hypertension and end-organ damage. Early recognition of retinal changes remains an important step in the risk stratification of hypertensive patients.

Retinal microvascular abnormalities and cognitive impairment in middle-aged persons: the Atherosclerosis Risk in Communities Study

BACKGROUND AND PURPOSE

Cerebral microvascular disease has been hypothesized to contribute to cognitive impairment, but few clinical data are available. Here, we examine the relation of retinal microvascular abnormalities with cognitive function in middle-aged persons free of stroke.

METHODS

The Atherosclerosis Risk in Communities Study is a population-based study with examinations every 3 years from 1987 through 1998. At visit 3, when participants were 51 to 70 years of age, retinal photographs were obtained and evaluated for retinal microvascular abnormalities according to standardized protocols. Cognitive function was assessed with standardized tests (Delayed Word Recall Test, Digit Symbol Subtest, and Word Fluency Test) at visits 2 and 4 and averaged for analysis. Persons with stroke or taking central nervous system-relevant medications were excluded, leaving 8734 with data for this study.

RESULTS

After education, diabetes mellitus, blood pressure, carotid intima-media thickness, and other risk factors were controlled for, retinopathy was associated with lower cognitive test scores. The adjusted odds ratios for persons with Delayed Word Recall scores 2 SD or lower than the mean were 2.60 [95% confidence interval (CI), 1.30 to 2.91] for any retinopathy, 3.00 (95% CI, 1.81 to 4.98) for microaneurysms, 3.39 (95% CI, 1.99 to 5.78) for retinal hemorrhage, and 3.07 (95% CI, 1.53 to 6.17) for soft exudates. Results were similar for the other 2 cognitive tests and in people with and without diabetes and hypertension.

CONCLUSIONS

Retinopathy is independently associated with poorer cognitive function in middle-aged persons without stroke, suggesting that cerebral microvascular disease may contribute to the development of cognitive impairment.

Association between medial temporal lobe atrophy on CT and parietotemporal uptake decrease on SPECT in Alzheimer's disease

OBJECTIVES

Alzheimer's disease is the most frequent cause of degenerative dementia. Despite the available diagnostic criteria, improvement of diagnosic accuracy is still required. The aim of this prospective study was to assess in a large population of patients referred to a memory clinic the diagnostic value of the combination of medial temporal lobe atrophy on temporal oriented CT and decreased temporoparietal uptake on HMPAO single photon emission tomography (SPECT).

METHODS

The study was conducted in 125 patients aged 51-93: 64 with probable Alzheimer's disease (Mean (SD) mini mental state examination (MMSE)=18.34 (6.93)), duration of disease=6.48 (2.93) years, 13 possible Alzheimer's disease (MMSE=21.58 (5.48), duration of disease=6.08 (2.56)), 48 patients with miscellaneous memory disorders (MMSE=21.98 (6.10), duration the disease = 6.85 (3.91)).

RESULTS

For the diagnosis of probable Alzheimer's disease, the sensitivity of this association was 0.56, the specificity 0.93, the positive predictive value 0.95, and the negative predictive value 0.45. The diagnosic accuracy was 0.68. Both medial temporal atrophy and parietotemporal decrease in uptake were present in four of 13 patients with possible Alzheimer's disease and 11 of 48 with miscellaneous memory disorders. The association was absent in 27 of 29 patients with frontotemporal dementia. In mild stages (MMSE>18; n = 32), the sensitivity of the association was 0.34, the specificity 0.93, the positive predictive value 0.85, and the negative predictive value 0.57. The diagnosic accuracy was 0.53.

CONCLUSION

This association, although not sensitive, helps to select patients with high probability of Alzheimer's disease at an early stage which can be of interest for clinical and research purposes.

Usefulness of follow-up regional cerebral blood flow measurements by single-photon emission computed tomography in the differential diagnosis of dementia

The aim of this study was to evaluate whether follow-up measurements of regional cerebral blood flow (rCBF) by single-photon emission computed tomography (SPECT) provide additional information in the differential diagnosis of dementia. Thirty-six patients (70 +/- 14 yr) with suspected dementia who had two technetium 99m-hexamethylpropyleneamineoxime SPECT scans over 18 +/- 7 months were included in this retrospective study. The patients comprised three groups based on the final clinical diagnosis: (1) neurodegenerative disorder (NDD) including Alzheimer's disease (AD) (n = 13), frontotemporal lobe dementia (n = 2), progressive supranuclear palsy (n = 1), and mixed dementia (AD plus multiinfarct dementia [MID]) (n = 3); (2) MID (n = 8); and (3) psychiatric disorders (depression [n = 7], psychosis [n = 1], and anxiety [n = 1]). Blinded to the clinical diagnosis and using visual analysis, the nuclear medicine physicians compared the second scan with the first scan for each patient to characterize temporal changes in rCBF. SPECT findings were categorized into three patterns of rCBF change: worsened, improved, and unchanged. Of the worsened rCBF group, 17 (85%) belonged to the NDD group whereas 2 (10%) and 1 (5%) belonged to the MID and psychiatric disorders groups, respectively. All 5 (100%) of the improved rCBF patients belonged to the psychiatric disorders group. Thus, worsening of rCBF favors the diagnosis of NDD whereas improvement in rCBF may mitigate against the diagnosis of NDD or MID. Follow-up rCBF measurements by SPECT thus provided additional information on the possible cause of dementia. A prospective study to further evaluate the usefulness of follow-up rCBF measurements by SPECT appears warranted.

Single photon emission computed tomography in dementia: relationship of perfusion to cognitive deficits

Sixteen patients with dementia (nine with Alzheimer's disease and seven with multi-infarct dementia) were studied with xenon-133 and hexamethyl-propyleneamine-oxime single photon emission computed tomography (SPECT). Quantification of cerebral blood flow was determined in 16 hemispheric regions of interest. Neuropsychological deficits were assessed with the Mini-Mental State Examination and the Neurobehavior Cognitive Status Examination. Alzheimer's disease patients had symmetric reduction of parietal lobe perfusion; multi-infarct dementia patients had multifocal perfusion deficits. Correlations were demonstrated between cerebral blood flow in the posterior brain regions and performance on tests of language, memory, attention, figure copying, judgment, and similarities. Alzheimer's disease patients exhibited more language impairment than multi-infarct dementia patients. SPECT promises to provide diagnostic information and data relevant to interpretation of neuropsychological deficits.

Differentiation of multi-infarct and Alzheimer dementia by intracranial hemodynamic parameters

BACKGROUND AND PURPOSE

The differentiation between the Alzheimer and multi-infarct types of dementia may still be equivocal considering clinical criteria, neuropsychological tests, and imaging techniques. Cerebral microangiopathic alterations underlying multi-infarct dementia should allow the characterization of dementia subgroups.

METHODS

Patients with a diagnosis of multi-infarct dementia (n = 17; mean age, 69.1 +/- 8.5 years) or Alzheimer dementia (n = 24, mean age, 65.8 +/- 9.0 years) according to standard testing criteria, clinical findings, and neuroimaging techniques (computed tomography and magnetic resonance imaging) were investigated prospectively by transcranial Doppler sonography and compared with a normal reference group (n = 64; mean age, 61.0 +/- 11.1 years). Transcranial Doppler sonography allows an indirect evaluation of peripheral flow resistance in the microcirculatory bed by quantifying pulsatility characteristics, as reflected in the effective pulsatility range (time-averaged mean blood flow velocity minus the peak-systolic to end-diastolic amplitude, in centimeters per second).

RESULTS

A total of 204 vessels were investigated in 105 subjects. Mean and diastolic blood flow velocities as well as the effective pulsatility range were significantly lower in the multi-infarct dementia group compared with the Alzheimer and the normal reference groups (p < 0.001). By using receiver operating characteristic analysis, a cutoff point for effective pulsatility range values of -5 cm/sec gives a side-dependent sensitivity of 90.48-95.24% and a specificity of 64.71-70.59% in diagnosing Alzheimer-type dementia; the corresponding sensitivity and specificity for a value of -2 cm/sec are 82.35-88.24% and 80.95-90.48%, respectively.

CONCLUSIONS

Pulsatility changes as reflected by the effective pulsatility range are a noninvasive additional criterion in the differential diagnosis of dementia.

Spectral analysis of the EEG and 99m-Tc-HMPAO SPECT-scan in Alzheimer's disease

99m-technetium-hexamethylpropylene-amineoxine (99m-Tc-HMPAO) single-photon-emission-computer-tomography (SPECT)-scans and spectral analyzed electroencephalogram (EEGs) of 20 patients with Alzheimer's disease (AD) were studied. A significant correlation was found between the temporoparietal-cerebellar-ratio (TP/C-ratio) of the SPECT-scan and the peak frequencies of leads T3-T5, C3-P3, and C4-P4 of the EEG. In addition a significant negative correlation between the TP/C-ratio and the theta/alpha-ratio (t/a-ratio) of leads T3-T5, T4-T6, C3-P3, and C4-P4 was demonstrated. Our study demonstrates that slowing of the EEG parallels a decrease in blood flow in the temporoparietal regions in AD-patients. Both findings could be parallel phenomena of regional hypometabolism.

Muscarinic and nicotinic contributions to cognitive function and cortical blood flow

Muscarinic receptor blockade in humans induces a transient memory deficit claimed to mimic aspects of Alzheimer's disease (AD). AD is also strongly associated with a specific blood flow abnormality in parietotemporal cortex; we previously showed that, despite induction of a dementia-like state, scopolamine does not produce these blood flow changes. In the present study, we administered both muscarinic and nicotinic receptor blockade (using scopolamine and mecamylamine) to seven elderly healthy subjects and measured subsequent changes in cognition and cortical perfusion, using the 133Xe inhalation method to quantify regional cerebral blood flow (rCBF). Results confirmed earlier findings of scopolamine-induced memory deficit and frontal cortex flow reduction. Only mecamylamine, however, produced a perfusion deficit in parietotemporal cortex. All effects were transient and dose-dependent. These findings demonstrate the safety and feasibility of differential and combined blockade of nicotinic and muscarinic cholinergic blockade in human subjects. Furthermore, the nicotinic antagonist mecamylamine yields rCBF changes similar to those seen in AD, despite producing only minimal cognitive effects on its own. The rCBF and behavioral manifestations in AD may therefore reflect the functional loss of nicotinic receptors in addition to alterations in other receptor systems.

Cortical circumferential profile of SPECT cerebral perfusion in Alzheimer's disease

We developed a semiautomatic method termed "cortical circumferential profiling" for objective analysis of cerebral cortex function in emission tomographic neuroimaging studies. This method treats cortex as a continuous ring near the outer brain edge. A computer algorithm samples the cortex at 60 contiguous, equiangular locations, using 1-cm2 samples. These values are plotted as a function of cortical angle to produce the cortical circumferential profile. This method was used in a study of regional cerebral perfusion in 15 patients with Alzheimer's disease and 8 elderly control subjects using N-isopropyl[I-123]-iodoamphetamine. Cortical circumferential profiling decreases variability, examines the entire cortex within slices at preselected levels above the orbital-meatal line, and facilitates intrasubject and intersubject comparisons.

SPECT in the diagnosis of Alzheimer's disease and multi-infarct-dementia

SPECT with Tc-99m HM-PAO as a radiopharmaceutical was performed in 17 patients meeting research criteria for Alzheimer's disease (AD), in 10 patients with a clinical diagnosis of multi-infarct-dementia (MID) and in 12 healthy volunteers. Regional tracer uptake was measured in frontal, parietal, and temporoparietal regions. A statistically significant decrease of tracer uptake in the temporoparietal region was found in AD-patients compared with controls. AD-patients showed less activity in this region than MID-patients, but this difference did not reach statistical significance. In both AD- and MID-patients decrease of tracer uptake was not correlated with dementia severity. We conclude that SPECT brain imaging is not yet ready for routine use in the distinction between AD and MID.