Discussion
Our study shows that patients with a prior history of hypertension and dyslipidaemia as well as those who appear as untreated/undiagnosed for these risk factors on admission are more likely to present with a lower NIHSS score at admission. These patients were also more likely to present with small vessel disease or subcortical stroke. This may in part explain the lower NIHSS at presentation. However, for patients with prior histories hypertension and dyslipidaemia, their prognosis at 90 days was worse compared with patients without these risk factors and those who were undiagnosed for these risk factors at the time of admission. Further analysis revealed that age and hypertension were strongly associated with a high mRS score (3–6) at 90 days, adjusting for covariates. Conversely, the male sex, prior antidiabetic therapy and undiagnosed diabetes were protective against a high mRS score at 90 days.
Similar to other studies that have reported the adverse effects of diabetes on ischaemic stroke outcomes,16 17 we observed a better prognosis at 90 days (lower mRS scores) for patients with undiagnosed diabetes compared with patients with diabetes. Similarly, multivariate regression analysis revealed that patients with undiagnosed diabetes were 0.46 times less likely to develop a higher mRS score at 90 days. This may be because the ‘undiagnosed’ diabetics had milder disease. The undiagnosed diabetes had a median (IQR) HbA1c of 6.2 (5.9–7.2) compared to patients with diabetes 8.5 (7.0–10.4). High levels of HbA1c, that is, ≥6.5, have been demonstrated to be significantly associated with poorer neurological outcomes (adjusted OR of 2.387, 95% CI 1.201 to 4.745).18 Similarly, Lei et al19 reported that patients with a HbA1C >8.3 had significantly higher rates of mortality at 3 months (p=0.012) and 1 year (p=0.034). Interestingly, the use of antidiabetic therapy seemed to be protective against poor ischaemic stroke outcomes. Mima et al20 have previously reported that administration of metformin in diabetes mellitus patients prior to stroke onset may be associated with reduced neurological severity (OR 11.3, p=0.046). Similarly, we have shown that prestroke treatment with metformin improved the mRS at 90 days outcome by a factor of 0.14 (incidence risk ratio of 0.86, p=0.006).21 In our current study, the use of antidiabetic therapy prior to admission was protective against a higher mRS score at 90 days (adjusted OR 0.52, 95% CI 0.34 to 0.79).
Previous reports suggest that patients with dyslipidaemia may have better outcomes following an acute stroke.22 23 In the SPARCL trial,24 a 13.7 mg/dL increase in HDL was associated with a 13% reduction in ischaemic stroke risk as well as major adverse cardiac events. Similarly, Ali et al25 reported a 2.27-fold higher mortality rate in the low-normal HDL group compared with the high HDL group (p=0.049) as well as a higher 1-year stroke recurrence rate for the low-normal HDL group (p=0.034). Similarly, in our study, known dyslipidaemia and undiagnosed dyslipidaemia were not strongly associated with a higher mRS score at 90 days after adjusting for covariates (adjusted OR 1.00, 95% CI 0.80 to 1.26 and adjusted OR 0.93, 95% CI 0.71 to 1.24).
Our study also showed that males were 0.56 times less likely to have an mRS score of 3–6 at 90 days compared with females (p<0.001). This is likely secondary to the younger age of the predominantly younger expatriate male population in Qatar (the median age of males in our study was 53 compared with 63 for females). There are additional biological differences that may explain this effect. It has been reported that women and men differ in their baseline functional status during their first stroke onset, with the former exhibiting a poorer functional baseline.26 This is attributed to females’ older age during their first stroke episode27 and living arrangements whereby females tend to live alone.28 Females are also more predisposed to obesity29 and hypertension.30 In addition, the male patients were younger, were more likely to have small vessel disease and had lower NIHSS at admission. These factors may contribute to the better outcome at 90 days.
In our study, we also observed that patients with undiagnosed risk factors for diabetes, hypertension and dyslipidaemia, all had lower mRS scores at 90 days compared with patients with known risk factors. One reason for this is that a higher proportion of patients from these undiagnosed risk factor categories presented with small vessel disease compared with the known risk factors group. Several studies have reported that patients who present with small vessel disease have a better outcome than patients diagnosed with strokes or other aetiologies. In a study composed of 1816 patients, Arsava et al31 reported that regardless of the etiologic stroke classification system used (CCS vs TOAST vs ASCO), patients with small artery occlusion all had the lowest 90 day cumulative mortality risk (p<0.001) compared with large artery atherosclerosis, cardiac embolism, strokes of uncommon causes and undetermined causes. Markaki et al32 also reported that the 1-year and 4-year mortality rates were lowest for patients with small artery occlusion compared with patients with large artery atherosclerosis, cardioembolic stroke and patients with strokes of unknown aetiology. However, in a retrospective analysis of 538 patients, Wei et al33 observed the 90-day mortality rate to be highest among patients with small artery occlusion (28.57%) compared with 12.5% for patients with stroke of other determined causes and 10.21% for large artery atherosclerosis (p<0.001). A potential explanation for this discrepancy is that none of the patients enrolled in this study had a minor stroke, therefore, they may be more prone to poorer outcomes. Another rationale is that for patients with known risk factors, their conditions might be more severe than patients with no risk factors and undiagnosed risk factors, which might predispose them to higher mRS scores.
Although some studies have reported hypertension to be protective against mortality after stroke, we found a strong association between hypertension (adjusted OR 1.44, 95% CI 1.07 to 1.96) and a higher mRS score at 90 days but not undiagnosed hypertension (adjusted OR 1.49, 95% CI 0.95 to 2.33). In several observational studies, both extremes of high and low BP values are associated with poor outcomes following stroke.34 35 After an ischaemic episode, a penumbra of viable brain tissues exists around the infarcted area and an acute hypertensive response can be beneficial in this instance as it preserves the cerebral blood flow to the hypoperfused area.36 Conversely, high BP can increase the risk of oedema formation, haematoma enlargement and haemorrhagic transformation in ischaemic stroke.37 Perhaps there is an optimal range of BP and depending on patient characteristics, having a history of hypertension can be beneficial for some but adverse for others. In our study, we did not collect data on the duration of our patients’ hypertension, therefore, depending on how long they had this condition for, this can be associated with a low or high mRS score at 90 days. Future studies should examine how the duration of hypertension can affect patients’ outcomes following ischaemic stroke. We also did not observe a significant association between smoking history and higher mRS score at 90 days (adjusted OR 0.92, 95% CI 0.73 to 1.15). A potential explanation for this is that smokers are more likely to be younger and are more likely to experience small vessel disease compared with other stroke subtypes.38 Indeed, in our study, smokers were significantly younger than non-smokers (p<0.001).
There are several limitations to our study. First, we do not know the duration of the diabetes, hypertension and dyslipidaemia prior to the acute stroke or how well these conditions were treated prior to the stroke, although such data are often difficult to collect and have inherent inaccuracies, that is, recall biases. There were other risk factors that we did not assess in our study such as history of atrial fibrillation, ischaemic heart disease, congestive heart failure, valvular heart disease and usage of prior antithrombotic prior to stroke onset. We also had missing data for the mRS score at 90 days on 2249 patients (out of 9479). Since Qatar’s population is composed of mainly of expatriate workers, it is impossible to collect data for everyone as they may have moved back to their home country once their work contract ended. Our patient sample is also composed of largely Middle Eastern ethnicity (Qatari, Arabs), South Asian and Far Eastern (Asians), therefore, our results might have differed if we recruited patients of other ethnicities. However, given the large sample size of our study and the prospective design, we believe our results provide valuable information on ischaemic stroke outcomes between patients with known risk factors and those with undiagnosed and/or no known risk factors. Lastly, we did not collect patient’s level of education, household income, geographical location and occupation, which could inform us of patients’ awareness of stroke risk factors as well as capacity to access care/services to manage these conditions.