Abstract
Dear sir I read with great interest the article by Sturm and Macdonell (1), in which they presented a patient with recurrent thunderclap headache associated with reversible intracerebral vasospasm causing stroke. This hypertensive patient acutely presented with headache followed by alteration in mental status function and possibly, along with cortical blindness (authors did not mention light reflex). Magnetic resonance (MR) imaging showed white matter changes, dominantly in parieto-occipital regions. In due course, the patient showed considerable improvement in clinical features as well as in imaging abnormalities. In fact, in this patient the clinical syndrome and imaging abnormalities are consistent with the diagnosis of a newly recognized ‘posterior leukoencephalopathy syndrome’ which predominantly affects the cerebral white matter. This acutely evolving neurological condition is clinically characterized by headache, nausea and vomiting, seizures, cortical visual disturbances, altered mental status and occasionally focal neurological deficits (2–6). Posterior leukoencephalopathy syndrome is often associated with an abrupt increase in blood pressure and usually seen in patients with eclampsia, renal diseases, and in patients with hypertensive encephalopathy. It is also seen in patients treated with cytotoxic and immunosuppressive drugs such as cylosporine, tacrolimus and interferon-alpha. The lesions of posterior leukoencephalopathy can be seen with computed tomography (CT) but they are better visualized with magnetic resonance imaging (MRI). T2-weighted MR images show, predominantly, white matter hypodensity, characteristically involving the parieto-occipital regions. In patients with extensive involvement other structures like brainstem, cerebellum, basal ganglion and frontal lobes can also be affected. The imaging abnormalities are often symmetric, though asymmetric involvement is not unusual. At times, grey mater of brain is also extensively affected. Frequently, the syndrome of posterior leukoencephalopathy may be difficult to distinguish from simultaneous bilateral posterior cerebral territory infarction caused by ‘top of basilar embolism’. It is of paramount importance to distinguish both these conditions, because in case of ischaemic stroke most treatment guidelines recommend (7) that mild to moderate hypertension should not be treated. In contrast, treatment of hypertension in patients with posterior leukoencephalopathy is essential to reverse the pathogenic process before it progresses to cause permanent brain injury (8).
The exact aetiopathogenesis of posterior leukoencephalopathy syndrome is not precisely known. This syndrome, possibly, results from a rapid rise in blood pressure (which might have gone unnoticed in the patient described by Sturm and Macdonell) that overcomes the brain's normal ability to autoregulate cerebral blood flow. This disturbance in cerebral blood flow autoregulation produces dilatation of cerebral arterioles with opening up of endothelial tight junctions of blood–brain barrier and leakage of plasma and erythrocytes into the extracellular space producing cerebral oedema. According to another hypothesis, patients with posterior leukoencephalopathy develop vasospasm of intracerebral vessels secondary to sudden elevations in blood pressure and, subsequently, ischaemia of the brain tissue. Ischaemic damage first produces cytotoxic oedema and then extracellular oedema (possibly responsible for producing headache in this patient). As has been observed in the present case, reversibility of imaging and clinical abnormalities with immediate treatment is consistent with the hypothesis of vasospasm for this syndrome. Adrenergic sympathetic innervation of cerebral vessels is an important component in physiological mechanisms of cerebral blood flow autoregulation. The vessels of the carotid system are better supplied with sympathetic adrenergic innervation than those of the vertibro-basilar system. This inherent deficiency of adrenergic innervation possibly results in loss of vasoconstrictor properties of cerebral blood vessels, mainly in posterior cerebral areas producing the syndrome of posterior leukoencephalopathy (4–6).
So, clinicians must be aware of this syndrome as its recognition obviates unnecessary diagnostic procedures (as authors were also thinking of doing brain biopsy); moreover, this syndrome is potentially reversible by prompt lowering of elevated blood pressure.