There are no universally accepted guidelines for the diagnosis of vascular parkinsonism, but based on clinical findings and pathology, Zijlmans et al. have proposed the following criteria: a) parkinsonism, b) cerebrovascular disease visible on MRI or CT, and c) a relation between a) and b), either in the form of acute hemiparkinsonism resulting from infarction or haemorrhage in the nigrostriatal pathway (subtype 1), or small vessel disease in the white matter with gradual development of parkinsonism (subtype 2) (15). Typically, brain MRI is necessary to determine whether there is damage to the nigrostriatal pathway (Figure 1) or small vessel disease in the white matter (Figure 2). CT scans of the brain are less suitable for making the diagnosis due to their lower sensitivity for lacunar infarcts and small vessel disease (5).
Vascular parkinsonism and Parkinson's disease differ in terms of prognosis and treatment response, and therefore it is important to distinguish between them. Patients with vascular parkinsonism usually present with difficulty walking, but show less flexion of the trunk, hips and knees, and better forward arm swing than patients with Parkinson's disease (16). Patients with Parkinson's disease typically present with asymmetric symptoms in the upper extremities. Cognitive impairment and urinary incontinence are more common in cases of vascular parkinsonism (17), whereas resting tremor and olfactory impairment are more common in Parkinson's disease (9, 18).
Vascular parkinsonism subtype 2 differs from Parkinson's disease in terms of prognosis, with earlier and more frequent need for walking aids (3, 5) and, according to a prospective cohort study, significantly shorter life expectancy (19). In addition, dopaminergic medications are less effective in vascular parkinsonism than in Parkinson's disease, although responses are somewhat better in subtype 1 than subtype 2 (12, 13, 20).
Differences between vascular parkinsonism and Parkinson's disease are also seen on brain imaging. In cases of vascular parkinsonism, brain MRI will reveal infarction, haemorrhage, or signs of small vessel disease. In Parkinson's disease, brain MRI can appear completely normal, although elderly patients may have vascular changes as incidental findings; however, these will be much less abundant than in cases of vascular parkinsonism (20, 21). A dopamine transporter scan (DaTSCAN) is a nuclear medicine procedure that shows changes in brain dopaminergic activity, and that can be used to detect degeneration of nigrostriatal nerve endings. DaTSCAN always shows pathological changes in Parkinson's disease, whereas in cases of vascular parkinsonism DaTSCAN is often normal if the nigrostriatal pathway is not directly affected (5).
Despite the differences between vascular parkinsonism and Parkinson's disease, many patients are probably misdiagnosed. In a post-mortem study of 28 patients with vascular parkinsonism, only six had been correctly diagnosed (14), while an autopsy study of 39 patients with parkinsonism found that five had vascular aetiology that had gone unrecognised antemortem (22). Other studies have suggested that vascular parkinsonism may be among the most common differential diagnoses of Parkinson's disease (23, 24).
Vascular parkinsonism can also be difficult to distinguish clinically from multiple system atrophy. Both conditions typically cause difficulty walking, falls and urinary dysfunction. However, patients with multiple system atrophy will have parkinsonism in the upper extremities and will often develop additional symptoms such as dystonia in the neck muscles, with antecollis, dysphagia and dyspnoea (25).