Detecting Alzheimer's disease

Evaluation of the cholinergic hypothesis in Alzheimer's disease with neuropsychological methods

AIM

This study aimed at evaluating the cholinergic hypothesis in Alzheimer's disease (AD) patients utilizing the pupillometry method, cognitive tests and Hamilton Depression Rating Scale (HAM-D), as well as to examine whether a correlation between cognitive tests and pupillometry exists.

METHODS

Forty-two patients with mean age 69.2 ± 7.0 years and documented AD volunteered to participate in this study, while 33 healthy matched subjects served as controls. All subjects underwent a pupillometric measurement and performed the Wechsler Memory Scale (WMS) and Mini Mental State Examination (MMSE). Also, HAM-D was used to assess the severity of depressive symptoms. The pupillometric parameters studied were (1) latency for the onset of constriction (T1), (2) maximum constriction velocity (VCmax), and (3) maximum constriction acceleration (ACmax).

RESULTS

In AD patients MMSE and WMS score were correlated with ACmax (r = -0.409, p < 0.05 and r = -0.513, p < 0.05, respectively) and VCmax (r = -0.664, p < 0.05 and r = -0.771, p < 0.05), respectively. Moreover, T1 was found to be significantly increased by 23 % (p < 0.05) in AD patients compared to healthy subjects. Conversely, the mean scores of VCmax and ACmax were significantly decreased in AD patients by 46 % (p < 0.05) and by 47 % (p < 0.05), respectively, as compared to healthy subjects. There was no significant difference between the two groups for HAM-D. Additionally, AD patients showed decreased score in WMS by 40 % (p < 0.05) and in MMSE by 28.5 % (p < 0.05) compared to healthy subjects. Of the indices that were studied VCmax and ACmax are governed mainly by the action of the Parasympathetic Nervous System.

CONCLUSIONS

The results of this study demonstrated that there is a correlation between cognitive tests and pupillometry in AD patients. Thus, pupillometry could be considered as a sensitive technique for the investigation of cholinergic deficits, which indirectly lead to memory and cognitive disorders in AD patients.

Pupil response biomarkers distinguish amyloid precursor protein mutation carriers from non-carriers

CONTEXT

Alzheimer's disease (AD) is usually only diagnosed many years after pathology begins. Earlier detection would allow emerging interventions to have a greater chance to preserve healthy brain function. A rare form of Alzheimer's disease, caused by autosomal-dominant mutations, affects carriers with 100% certainty and at a younger age specific to their mutation. Studying families with these mutations allows a unique investigation of the temporal sequence of biomarker changes in Alzheimer's disease.

OBJECTIVE

To determine whether the pupil flash response (PFR), previously reported to be altered in sporadic Alzheimer's disease, is different in pre-symptomatic mutation carriers.

DESIGN

Researchers blinded to participant mutation status collected pupil response data from cognitively normal participants in the Dominantly Inherited Alzheimer's Network (DIAN) Study during 2010-2011.

SETTING

The pupil response was examined at the McCusker Alzheimer's Research Foundation in Perth, Western Australia.

PARTICIPANTS

Participants were from a single family harboring an Amyloid-Beta Precursor Protein genetic mutation (APPGlu693Gln). Six carriers and six non-carriers were available for pupil testing (age 43.0±8.3 years old, 2 males and 10 females, 4 with hypertension).

MAIN OUTCOME MEASURE

Pupil response parameter comparison between mutation carriers and non-carriers.

RESULTS

75% recovery time was longer in mutation carriers (p<0.0003, ROC AUC 1.000, Sensitivity 100%, Specificity 100%) and percentage recovery 3.5 seconds after stimulus was less in mutation carriers (p<0.006, ROC AUC 1.000, Sensitivity 100%, Specificity 100%).

CONCLUSIONS

PFR changes occur pre-symptomatically in autosomal dominant AD mutation carriers, supporting further investigation of PFR for early detection of AD.

Cholinergic deficiency in Alzheimer's and Parkinson's disease: evaluation with pupillometry

The aim of the study was to evaluate the cholinergic deficiency in Alzheimer's (AD) and Parkinson's disease (PD). For this purpose, pupil size changes and mobility were assessed using a fast-video pupillometer (263 frames/s). Twenty-three (23) patients with probable AD and twenty-two (22) patients with PD (eleven with cognitive impairment and eleven without) entered the study. A full record of the pupil's reaction to light was registered. From this data ten (10) parameters were measured and reported. Comparison of those parameters in both group of subjects followed. Patients with probable AD had abnormal pupillary function compared to healthy ageing. All the Pupil Light Reflex (PLR) variables significantly differed between the two groups (p<0.005) except the Baseline Pupil Diameter after 2-min dark adaptation (D1) and the Minimum Pupil Diameter (D2). Maximum Constriction Acceleration (ACmax) was the best predictor in classifying a subject as normal or as an AD with a perfect classification ability (AUC=1, p<0.001). ACmax and Maximum Constriction Velocity (VCmax) were significantly lower in PD patients without and with coexisting cognitive impairment compared to normal subjects (p<0.001). Patients with cognitive impairment had significantly lower levels of ACmax, VCmax and amplitude (AMP=D1-D2) than patients with no cognitive deficits. ACmax and secondarily VCmax were the best predictors in classifying a subject as normal or as a PD patient with or without cognitive impairment. Cognitive and memory impairment, which reflects a cholinergic deficit, may be a crucial pathogenetic factor for the decrease in the aforementioned pupillometric parameters. VCmax and ACmax can be considered as the most sensitive indicators of this cholinergic deficiency.

Pupillary cholinergic hypersensitivity predicts cognitive decline in community dwelling elders

Previous research demonstrated that it is possible to distinguish patients with probable Alzheimer's disease from age-matched controls based on an exaggerated pupil dilation response to dilute tropicamide. The research reported here employed a prospective longitudinal design to follow over time (2-4 years) a sample of 55 community dwelling elders with and without an exaggerated pupil response using the pupil assay and a comprehensive battery of neuropsychological tests sensitive to pre-clinical AD. Discrete time survival modeling was used to assess the ability of the assay to predict a pattern of cognitive decline consistent with early AD. Analysis showed that there is an increased risk (odds ratio of 3) with a hypersensitive pupil response (>/=13% increase in pupil diameter over baseline diameter) for developing significant cognitive impairment in areas of memory attention and language in a pattern, consistent with pre-clinical Alzheimer's disease. When controlling for ApoE allele type the odds ratio for pupil response as a risk factor increased to 4. The analysis also found that an exaggerated pupil response was a significant (p=.02) predictor of cognitive decline. This analysis of longitudinal data has shown that over time an exaggerated response on the pupil assay is a significant independent risk factor for developing pre-clinical Alzheimer's disease. The risk for developing pre-clinical Alzheimer's disease is increased four-fold.

ApoE allelic variability influences pupil response to cholinergic challenge and cognitive impairment

Exaggerated pupil response to dilute tropicamide has been suggested as an early biological marker for Alzheimer's disease. The current study links apolipoprotein E (ApoE) allelic variability to the magnitude of pupil response in a sample of community-dwelling elderly without a diagnosis of Alzheimer's disease or dementia. Possession of an epsilon 4 allele influences both the likelihood of exhibiting an exaggerated pupil response above a predetermined cut-off (13% above baseline diameter) and the absolute overall magnitude of the response. Allelic variability was also shown to correlate with cognitive impairments in memory and attention. The data in this study further elucidate the nature of the biological bond between an exaggerated pupil response and the pathology of Alzheimer's disease. ApoE allelic variability is probably linked to pupil response through its influence on tau hyperphosphorylation. The early Alzheimer's pathology seen in the Edinger-Westphal area of cranial nerve III, a major centre for pupil control, is primarily tau-based with significant cell loss in this nucleus leading to central denervation hypersensitivity even in elderly who are clinically silent but who have early pathology.

Tropicamide effects on pupil size and pupillary light reflexes in Alzheimer's and Parkinson's disease

Diagnostic tests for Alzheimer's disease (AD) involving tropicamide blockade of cholinergic oculomotor functions were examined in AD patients (n=15), Parkinson's disease (PD) patients (n=15), and non-clinical control (NC) participants (n=15). Pupillographic methods were used to measure pupil diameter and pupillary light reflexes after double-blind ocular administration of dilute tropicamide (0.01%) in one eye and saline in the other eye. Changes in pupil size were measured in bright background light and near-darkness. Tropicamide increased pupil diameter to a similar extent in all three groups in light and darkness. Tropicamide also reduced the amplitude and latency of the pupillary light reflex to a similar extent for all three groups. Tropicamide pupillary response tests, therefore, were not sensitive or specific diagnostic tests for AD. Peak constriction amplitude of the pupillary light reflex was significantly reduced in both eyes in AD and PD groups relative to non-clinical controls, but AD and PD groups did not differ significantly. The pupillary light reflex test, therefore, was sensitive to AD, but lacked adequate specificity. Finally, peak constriction amplitude correlated significantly with dementia severity and donepezil treatment may have partially normalized pupillary light reflex abnormalities in AD patients. The pupillary light reflex test, therefore, may index central cholinergic dysfunction associated with disease progression and improvement in cholinergic function associated with pharmacologic treatment response in AD.

Selective cell loss in Edinger-Westphal in asymptomatic elders and Alzheimer's patients

Exaggerated pupillary response to a low concentration of cholinergic antagonists has been suggested as an early marker for Alzheimer's Disease (AD). To examine the anatomic basis of this phenomenon, we determined possible neuropathological changes in the Edinger-Westphal (EW) nucleus, a midbrain neural center with a significant functional role in the control of pupil size. Stereologically determined neuronal numbers within the EW were counted in individuals with pathologically confirmed AD, control cases with no AD-type pathology, and subjects with AD pathology not meeting diagnostic criteria for AD. The EW of AD patients displayed a marked and striking neuronal loss when compared with controls. In contrast, the number of neurons in the somatic portion of the nucleus of the third cranial nerve (NCNIII) remained intact. The EW in brains from clinically normal individuals with evidence of early AD-type pathology also displayed a significant and selective loss of neurons. The magnitude of EW neuronal loss in the latter group was smaller than that observed in AD. These findings suggest that pupillary hypersensitivity in AD may be caused by abnormalities in the EW. Neuronal loss and pathology within the EW in a subpopulation of clinically silent controls with pathologic findings consistent with early-stage AD constitutes a possible explanation for the reported exaggerated pupil response in some normal elderly subjects.

Changes in pupil reaction to light in Alzheimer's disease patients: a preliminary report

The aim of this preliminary study was to compare the pupil reaction to light in Alzheimer's disease (AD) patients before and after treatment and in normal controls. Ten AD patients diagnosed according to DSM-IV and NINCDS-ADRDA criteria (five medication-free and five under anticholinesterase treatment) and five age- and gender-matched controls took part in the study. Drug-free patients and all control subjects were free of any medication for at least four weeks. An optical method was used to assess the pupil reaction to a single flash. Medication-free AD patients manifested shorter latency and lower amplitude of maximum response to light in comparison to controls. These findings are in agreement with the presence of a cholinergic deficit in AD patients. Pharmacological treatment with donepezil, which is an anticholinesterase agent partially improves this deficit. The results of this preliminary investigation suggest that dynamic pupillometry could be a useful adjunct to assist the diagnosis of early AD, and the differential diagnosis between different types of dementia. AD patients seem to manifest a specific pattern of pupil reaction to light, and some characteristics of this pattern are detectable even in patients receiving anticholinesterase medication. However, this is only a preliminary report and further research is mandatory.

Tropicamide eyedrops cannot be used for reliable diagnosis of Alzheimer's disease

OBJECTIVE

To evaluate the mydriatic effect of tropicamide eyedrops as a diagnostic test for Alzheimer's disease.

MATERIAL AND METHODS

In a double-blind, placebo-controlled study, we assessed pupillary responses in 22 normal control subjects, 23 patients with probable Alzheimer's disease, 4 patients with isolated memory difficulty, and 6 patients with non-Alzheimer's dementia. Three separate studies were performed, the second and third on a subset of the original group. With use of infrared binocular pupillography, after 5 minutes of dark adaptation, we averaged pupil size during a 1-minute interval for baseline determinations. We then instilled 0.01% tropicamide into one eye. In the first two studies, we averaged pupil size for a 1-minute period at 5-minute intervals for 30 minutes, followed by a pupil light reflex test. In the third study, we measured pupil size every 5 minutes for 45 minutes and omitted the light reflex test.

RESULTS

No significant difference was noted in pupil dilatation between normal subjects and patients with Alzheimer's disease and between patients with non-Alzheimer's dementias and the Alzheimer's disease group in all three studies. Furthermore, on reperformance of the test in the same patients, more than 50% changed from a group above or below 13% pupil dilatation (a cutoff reported to distinguish Alzheimer's disease from normal control subjects) to the opposite group.

CONCLUSION

Results of this study indicate that pupil measurement after instillation of tropicamide cannot be used as a reliable diagnostic test for Alzheimer's disease. Moreover, test-retest reliability with use of dilute tropicamide eyedrops is questionable.

Pupillary response to tropicamide in Japanese patients with alcoholic dementia, Alzheimer's disease, and vascular dementia

The anticholinergic agent tropicamide causes a significantly greater change in the pupil diameter of patients with Alzheimer's disease (AD) than in that of patients with alcoholic or vascular dementia or in normal controls. Although the response increases with the severity of AD, the overlap of response with normal controls in milder cases and the difficulty of obtaining results in severe cases limit its use as a diagnostic tool.

Pupil response to tropicamide in Alzheimer's disease and other neurodegenerative disorders

Excessive mydriatic response to dilute tropicamide has been suggested as a possible non-invasive diagnostic test in patients with Alzheimer's disease (AD). To further evaluate the sensibility and specificity of this test we studied the pupillary response to tropicamide in 24 patients with AD, 30 age-matched controls, 7 patients with dementia other than AD and 13 patients with extrapyramidal disorders (EXD). Maximum dilatation response over baseline was much higher in AD with significant differences compared to controls (p < 0.001) and to EXD (p < 0.05). However, there was a quite wide range of overlap between AD and controls and no cut-off point was found with a high enough specificity to consider this a conclusive diagnostic test. Lower dilatation response in the overlapping range (13%), however, may be useful because of its negative predictive value (93.5%) and as a screening tool due to its sensitivity (87.5%).

The pupillary response to tropicamide in Alzheimer's disease

An increased pupillary response to a weak solution of tropicamide has recently been suggested to be diagnostic for Alzheimer's disease. If so, it would have far-reaching implications. We performed a masked study involving 17 patients with Alzheimer's disease and 20 mentally healthy controls with respect to the pupillary response induced by tropicamide. We found no significant difference in pupillary dilatation between patients and controls (19.7 +/- 11% versus 19.1 +/- 9%; p = 0.19).

Pupillary response to tropicamide in patients with Alzheimer disease

PURPOSE

To determine whether pupillary responses to dilute tropicamide could be used as a diagnostic test for Alzheimer disease (AD). The authors also investigated whether concurrent use of an oral acetylcholinesterase inhibitor (tacrine) alters the pupillary response to dilute tropicamide in patients with AD, and whether pupillary responses to dilute tropicamide differ in young versus older control subjects.

METHODS

Pupillary diameter and area of both eyes were measured in light and darkness, at 10-minute intervals for 40 minutes after random instillation of 0.01% tropicamide to one eye. Four groups of subjects were studied: 9 patients with AD, 10 who were treated with tacrine, 11 older control subjects, and 10 young control subjects.

RESULTS

Mean change in anisocoria was not significantly different among groups at any of the measurement time points. Mean percent change in diameter of the treated eyes showed a trend toward faster maximum dilatation in the AD groups, but change in pupillary measurements did not identify individuals with AD.

CONCLUSION

Pupillary response to dilute tropicamide did not effectively distinguish individual patients with AD from young or older control subjects.