Perplexing Perspectives of ICAD.

Intracranial atherosclerotic disease (ICAD) is the most common mechanism of ischemic stroke worldwide accounting for 30%-50% of strokes amongst Asians[1] and 8%-10% of strokes in Caucasians.[2] The described associations for ICAD in susceptible populations include race,[3] genes,[4] and vascular risk factors.[5] The mechanisms proposed in ischemia include artery-to-artery embolism, local branch occlusion, hemodynamic compromise resulting from progressive arterial narrowing or a combination of these factors.[6]

Why is ICAD more prevalent in Asians than that in Westerners; the reason for this is not completely known. Possible explanations include inherited susceptibility of intracranial vessels to atherosclerosis, acquired differences in the prevalence of risk factors and differential responses to the same risk factors. Lifestyle may play a role in racial–ethnic differences.[7]

Saraf et al. published a very important study in the current journal from South India comparing the data of stroke patients with ICAD between two major regional cohorts of South Indian and Chicago, USA.

Surprisingly in the current study, more patients with ICAD were recruited from Chicago in the defined time period contrary to the expectation of a higher number of ICAD patients from India, given the difference in the prevalence of ICAD between the regions.

The other demographic, clinical, and outcome parameters between the two cohorts were all as expected according to the published literature and add valuable data to understand the differences.

The stroke recurrence in the three-month outcome assessment, was more in Chicago cohort (21.7% vs 1.7%), and although a more rampant use of DUAT in South India cohort may explain the difference, more reasons need to be explored. Although ICAD is more sinister in terms of stroke recurrence, the extremely high rate of recurrent stroke in the Chicago cohort at 3 months (21.7%), assuming a better vascular risk factor control, compliance, follow-up, and stroke care pathways in the developed nation (Chicago cohort), looks unnerving!

This finding is even more surprising, given the recurrence rate of stroke from ICAD published in more recent trials (SAMMPRIS, 2011: 12.2% and TOSS-2, 2011: 4.4-6.5%).

The published risk factors for stroke recurrence amongst symptomatic ICAD include systolic blood pressure ≥140 mm Hg, cholesterol ≥200 mg/dl, metabolic syndrome, severity of stenosis ≥70%, poor collaterals, and black race.[67] Hence, assuming that in Chicago cohort the risk factors are well controlled and severity of stenosis was comparable in both regions, the reasons why the Chicago cohort sported a stroke recurrence of 21% remains enigmatically abstruse!

Overall, the study has a very important value addition for understanding and managing ICAD across two geographically, economically, and possibly ethnically different populations.