We read with interest the article by Jacobs et al 1 on stroke in the young. Their epidemiological work was carried out within the frame of the Northern Manhattan Stroke Study, a population-based registry, with comparisons between younger and older patients on demographic characteristics, risk factors, and prognosis, and with computation of the selective contribution of the younger patients to the burden of stroke. We conducted between 1994 and 1998 a similar study on 89 patients under 45 years

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... f age with a first-ever stroke documented by brain neuroimaging, in a defined population of central Italy. 2 Despite the inclusion in our study only of white subjects, we would like to make some comments and comparisons between the 2 studies. The overall stroke incidence in the white residents of the Northern Manhattan area was 10/100 000 per year. This figure was identical to that found in our study (10.2/100 000) and within the range of studies on subjects under 45 years of age (8.8 to 15/100 000) quoted by Jacobs et al. However, if we refer to the studies quoted in our article, that were all performed with a comparable methodology, the range was even tighter (9.3 to 14.8/100 000) and, if those are the true figures of stroke incidence in young whites, the much higher rates observed among Hispanics (26/100 000) and blacks (25/100 000) appeared even more impressive. A higher migration rate of Hispanic and black residents in the study area together with a higher fertility rate with respect to the white residents might have contributed to a disproportionate increase of younger age groups in those populations. In fact, we already showed that any variation of the age distribution may affect stroke incidence not only as a predictable consequence of changes in the proportion of elderly individuals within that population but also because of a variation of the stroke risk in the different age groups. 3 However, since patients eligibility relied on residency within the study area at least for 3 months before the event, while the study referral population was that reported by the 1990 US census, a biased estimation of the rate denominator might also have occurred for Hispanics and blacks. Degree of stability over time of the dynamic population should have been considered, accordingly. The proportion of strokes observed in whites under 45 years of age by Jacobs et al (2.5%) was almost identical to that found in our study (2.6%), while the corresponding proportions were 12.4% for Hispanics and 4.4% for blacks. Whichever was the factor increasing stroke incidence among younger Hispanics and blacks, it should have accounted for an anticipation of stroke occurrence rather than for an increase of the global stroke risk which should have been equally distributed among the younger and older age groups. Unexpectedly, Jacobs et al found similar 30-day case fatality rates in patients under (17%) and over (16%) 45 years of age, while in our study, the 30-day case fatality rate was lower (Pϭ0.005) in subjects under 45 years of age (11.2%) than in those over 45 years of age (26.0%). Since the case fatality rate is notoriously higher for intracerebral and subarachnoid hemorrhage with respect to ischemic stroke 4 and the proportion of ischemic stroke was lower in patients under 45 years of age than in those over 45, a higher incidence of hemorrhagic stroke in the study of Jacobs et al might have contributed to the lack of any difference in case fatality between younger and older patients.