Subcortical arteriosclerotic encephalopathy (Binswanger's disease)
Binswanger originally described eight cases of periventricular demyelination and dementia. This was considered a rarity until the advent of neuroimaging, and many patients with white matter changes on scanning acquired this diagnosis. Clinically, the features are very similar to those seen in patients with multiple subcortical infarcts, namely frontal and subcortical cognitive features, dysarthria, and pseudobulbar palsy. Gait impairment may occur early and is characterized by a wide-based shuffling gait, in contrast to the narrower base seen in Parkinson's disease (Thompson and Marsden 1987). Criteria have been suggested for the diagnosis of Binswanger's disease (Bennett et al. 1990).
Much confusion has arisen from attempts to diagnose Binswanger's disease from neuroimaging. Non-specific periventricular white matter abnormalities are common both in patients with dementia and in the non-demented elderly, and the term leuko-araiosis has been proposed (Hachinski et al. 1987).
Leukoaraiosis appears as low attenuation on CT scan, particularly around the frontal and occipital horns, and as increased signal on T2-weighted MRI. Neuropathologically, there is demyelination, gliosis, and hyalinosis, with fibrinoid necrosis of small blood vessels, similar to that seen in hypertension. Minor degrees of white matter disease are also seen in pure Alzheimer's disease.
Treatment is primarily that of management of vascular disease risk factors such as hypertension, smoking, diabetes, carotid stenosis, and heart disease. There have been few control trials of management of risk factors and its affect on cognition, but treatment of isolated systolic hypertension in the elderly may reduce the incidence of dementia (Forette et al. 1998).
Other causes of vascular dementia
Significant cognitive impairment, sufficient to justify the criteria of dementia, can occur after subarachnoid haemorrhage, subdural haematomas, and global ischaemia following cardiac arrest with laminar necrosis and hippocampal cell loss. A variety of vasculitides can also be associated with the early development of cognitive impairment and even present as a dementia; these include systemic lupus erythematosus (SLE) and primary cerebral angiitis, which is usually accompanied by headaches. Sneddon's syndrome (Rebollo et al. 1983) is the association of livedo reticularis with cerebrovascular disease, and can present with cognitive impairment. A number, but not all, are associated with anticardiolipin antibodies.
The rare cases of hereditary cerebral amyloidosis, both of the Icelandic and the Dutch and the Flemish type, can be associated with cognitive impairment, although the salient clinical feature is that of recurrent cerebral haemorrhage. Cerebral autosomal dominant arteriopathy with subcortical infarcts and leucoencephalopathy (CADASIL) (Dichgans et al. 1998) is characterized by recurrent subcortical ischaemic events with the subsequent development of a pseudobulbar palsy and cognitive impairment. Early symptoms include migraine-like headache and psychiatric disturbance.
The MRI scan shows a striking leucoencephalopathy in addition to multiple small infarcts. This condition, which is increasingly recognized, is linked to mutations in the Notch 3 gene (Joutel et al. 1996).