Title

Clinical and lifestyle determinants of asymptomatic intracranial atherosclerotic disease in adults undergoing MRI at two tertiary care centers in Karachi, Pakistan

Date of Award

2013

Document Type

Thesis

Degree Name

Master of Science in Epidemiology & Biostatistics (MSc Epidemiology & Biostats)

Department

Community Health Sciences

Abstract

The incidence of stroke has increased by 100% in the last four decades in developing countries like Pakistan. Intracranial atherosclerotic disease (ICAD) is the most frequent causative subtype of ischemic stroke in the world including Pakistan. ICAD is progressive narrowing of the arteries at the base of the brain due to atherosclerosis. After a stroke from ICAD, recurrence rate is highest in any sub-type of stroke, up to 28% with limited therapeutic options. Therefore, it is imperative to delineate the determinants of asymptomatic ICAD prior to stroke. Objective: The objective of this study was to identify the clinical, lifestyle, dietary and psycho-social determinants of asymptomatic Intracranial Atherosclerotic disease (ICAD) in adults undergoing MRI at two tertiary care settings in Karachi, Pakistan. Methodology: This observational cross sectional study was performed on 200 adult participants at the Radiology departments of two tertiary care centers of Karachi, Pakistan over a period of 3 months. The participants were first screened for stroke symptoms via the Questionnaire for Verifying Stroke Free Status (QVSS) by trained research officers. Those who did not report any stroke symptoms (QVSS —ve) were eligible to participate. The participants underwent a detailed medical history, socio demographic, lifestyle and anthropometric evaluation. All patients then received Magnetic Resonance Angiogram (MRA) All MRA scans were viewed centrally and calibrated on special software Dicom Viewer 3.0 used for calculating the degree, distribution of stenosis. Mean and standard deviations (SD) were calculated for continuous variables like age and BMI and proportions for categorical variables like education, ICAD, clinical and lifestyle factors. Principal Component Analysis was performed for Socio-Economic status (SES) and Dietary patterns and two major dietary patterns were identified; "prudent" and the "Western" patterns. An internationally standardized equation was used to calculate the degree of stenosis and intracranial stenosis was defined as any artery having >25% stenosis on MRA. The independent contribution of any risk factor to ICAD was examined in the Univariate and subsequent multivariable Cox proportional hazards algorithm and prevalence ratios and 95% confidence intervals were reported. Results: Of the 283 eligible participants approached, 200 participated in the study. Of these, asymptomatic ICAD was found in 34.5% (69) of the participants. Mean age of the participants was 37.13 (15.1) years with 62% (124) of the participants being younger than 45 years. There were an equal proportion of males and females in the sample population. Self-reported hypertension was 26.5%,(53) diabetes 9% (18) and dyslipidemia 5%(10) .ICAD was found to be most prevalent in people aged< 45 years, with higher levels of education, higher SES, increasing obesity, physical inactivity and western dietary pattern with increasing quintiles. Among the 3800 arteries studied of 200 patients, the posterior cerebral artery was found to be the most affected (42%; 37) ) followed by vertebral (34%; 30) and MCA (22.7%; 20).Significant stenosis (>50%) was found in 37.6% (32) of the arteries with 20% (17) being completely occluded. After adjusting for other independent variables, results of Cox Regression analysis showed that among the socio-demographic factors, higher SES was found to be significantly associated with asymptomatic ICAD, while smokeless tobacco and increasing quintiles of western dietary pattern were lifestyle factors significantly associated with ICAD. MRI associated findings of peri-ventricular lucencies were found to be significantly associated with ICAD. Conclusion: ICAD is a major public health problem with a burden of 34.5% in otherwise asymptomatic subjects. It preferentially affects the posterior circulation and is with modifiable lifestyle risk factors, mostly in younger individuals. Future studies to explore preventive interventions in our regions and to elucidate risks are needed.

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