Stroke, cerebrovascular diseases and vascular cognitive impairment in Africa

Abstract

With increased numbers of older people a higher burden of neurological disorders worldwide is predicted. Stroke and other cerebrovascular diseases do not necessarily present with different phenotypes in Africa but their incidence is rising in tandem with the demographic change in the population. Age remains the strongest irreversible risk factor for stroke and cognitive impairment. Modifiable factors relating to vascular disease risk, diet, lifestyle, physical activity and psychosocial status play a key role in shaping the current spate of stroke related diseases in Africa. Hypertension is the strongest modifiable risk factor for stroke but is also likely associated with co-inheritance of genetic traits among Africans. Somewhat different from high-income countries, strokes attributed to cerebral small vessel disease (SVD) are higher >30% among sub-Saharan Africans. Raised blood pressure may explain most of the incidence of SVD-related strokes but there are likely other contributing factors including dyslipidaemia and diabetes in some sectors of Africa. However, atherosclerotic and cardioembolic diseases combined also appear to be common subtypes as causes of strokes. Significant proportions of cerebrovascular diseases are ascribed to various forms of infectious disease including complications of human immunodeficiency virus. Cerebral SVD leads to several clinical manifestations including gait disturbance, autonomic dysfunction and depression. Pathological processes are characterized by arteriolosclerosis, lacunar infarcts, perivascular spaces, microinfarcts and diffuse white matter changes, which can now all be detected on neuroimaging. Except for isolated cases of cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy or CADASIL, hereditary arteriopathies have so far not been reported in Africa. Prevalence estimates of vascular dementia (2-3%), delayed dementia after stroke (10-20%) and vascular cognitive impairment (30-40%) do not appear to be vastly different from those in other parts of the world. However, given the current demographic transition in both urban and rural settings these figures will likely rise. Wider application of neuroimaging modalities and implementation of stroke care in Africa will enable better estimates of SVD and other subtypes of stroke. Stroke survivors with SVD type pathology are likely to have low mortality and therefore portend increased incidence of dementia.

Keywords: Africa; Alzheimer’s disease; Cerebrovascular disease; Small vessel disease; Stroke; Vascular cognitive impairment.

Figure 1. Stroke subtypes by the TOAST criteria in Africa

1A and 1B, Pathophysiology of stroke subtypes according to TOAST [1]. Figures show proportions (mean percent) of strokes resulting from large artery disease (LAD), CE, cardioembolic (CE), lacunar infarction or small vessel disease (SVD), other (Other) and undermined (Und) causes. 1A, In HICs, CE is the most common cause of strokes with SVD a little less frequent. Patients with CE having small infarcts commonly develop VaD. The frequency of ICH in these cohorts was a mean of 15% (range 9.6–14%). Chart was constructed from 13 different studies involving 12,931 patients from both hospital and non-hospital or community based cohorts in Western Europe and USA [14, 22, 27, 55, 57, 64, 74, 84, 113, 116, 130, 133, 144]. 1B, In SSA, SVD is the most frequent cause of stroke. All types of primary insults causing stroke or cerebrovascular disease can lead to cognitive impairment. Chart shows proportions of stroke pathophysiology collated from 5 different studies involving 2,843 patients from both hospital and community based cohorts in Ghana, Kenya, Nigeria, Mozambique, South Africa, Sudan, Uganda [59, 67, 79, 96, 109] The risk factors associated with particularly SVD include hypertension, diabetes mellitus, hyperlipidaemia, hyperhomocysteinaemia, chronic kidney disease, infection and obstructive sleep aponea. Lifestyle factors such as smoking, obesity, alcohol abuse and regular meat consumption are other factors. Abbreviations: CE, cardioembolic; HIC, high-income countries; LVD, large vessel disease; SSA, sub-Saharan Africa; SVD, small vessel disease; TOAST, Trial of Org 10172 in Acute Stroke Treatment; Und, undetermined. Chart 1A was adapted from [70].