Response to Letter by Sheikh
We appreciate the comments by Dr Sheikh. In our research letter,1 we studied the prevalence and associations of intracranial large-artery disease (ICLAD) among ethnic South Asians in Singapore. The cited reference “Global burden of intracranial atherosclerosis”2 for the statement reading “ICLAD is the most common vascular lesion in stroke worldwide” was published in the International Journal of Stroke, the official journal of the World Stroke Organization (WSO), edited by Prof Geoffrey Donnan, current president of the WSO. It is not registered with PubMed Central as its first issue was only published in February 2006.
The method of data collection was prospective with results noted as investigations were performed, rather than a retrospective review of the medical records. The descriptive data of age and gender in the Table 1 relates to the 188 patients with ICLAD assessed, whereas the data in paragraph one of the results relates to the whole study population of 200 patients. As stated in the article, the 12 patients who did not have ICLAD status described underwent neither any/adequate TCCD assessment nor magnetic resonance angiography. The multivariate analysis used was a linear stepwise regression, and the statistical software used was SPSS version 9.0.
This was a cross-sectional study of ethnic South Asians in Singapore. As such, we did not and cannot directly compare the stated 54% prevalence of ICLAD with other ethnicities. We maintain that this burden is high in view of the published findings of 24% prevalence of intracranial lesions among white stroke patients.3 With a 54% prevalence of ICLAD, a 10% prevalence of extracranial carotid severe stenosis/occlusion and a remaining 36% with neither of these, we conclude that ICLAD is the predominant site of disease among South Asian ischemic stroke patients in our study. The statement that “ICLAD was either asymptomatic or concurrent with small-vessel stroke” is a logical explanation for our finding of 27% ICLAD prevalence among small-vessel stroke.
The described association of ICLAD with hypertension is consistent with our cited reference and others.4–6 The explanation offered for the association between the inflammatory marker ESR and ICLAD was that “inflammation is believed to be involved in atherosclerosis pathogenesis”. The cited reference for this statement did involve C-reactive protein (CRP), another marker of inflammation. In view of the cross-sectional design of the study, we described associations only and did not assert any causal relationship. We dispute the dismissal of this data as “mere coexistence”. The associations described have biological plausibility and deserve to be tested for causality in other studies.
We described that the findings of this study “may be extrapolated to ethnic South Asians in urban regions of South Asia and large migrant ethnic South Asian populations living in developed countries” and made no suggestion that they be generalized beyond this. We concur that our results can serve to generate novel hypotheses in future investigation of this understudied ethnic group.
De Silva DA, Woon FP, Lee MP, Chen CPLH, Chang HM, Wong MC. South Asian patients with ischemic stroke. Intracranial large arteries are the predominant site of disease. Stroke. 2007; 38: 2592–2594.
Wityk RJ, Lehman D, Klag M, Coresh J, Ahn H, Litt B. Race and sex differences in the distribution of cerebral atherosclerosis. Stroke. 1996; 27: 1974–1980.
Yasak M, Yamaguchi T. Shichiri M. Distribution of atherosclerosis and risk factors in atherothrombotic occlusion. Stroke. 1993; 24: 206–211.