• Parkinson’s disease

The diagnosis of Parkinson’s disease (PD) is primarily a clinical exercise.1 Structural imaging is not recommended in cases with a typical presentation, and should remain reserved for those patients where there is reasonable doubt about the clinically based diagnosis.2 This is not uncommon: even in tertiary specialised centres, up to 25% of patients initially diagnosed with PD are reclassified at follow-up.3 Triggers to reconsider the diagnosis include presence of absolute exclusion criteria (such as cerebellar ataxia) or development of multiple features that jointly signal the presence of a form of atypical parkinsonism (‘red flags’). If neuroimaging is deemed necessary, brain MR is generally preferred over brain CT because of the superior resolution and sensitivity.4

Dopamine transporter single-photon emission CT (DaTscan) allows assessment of the nigrostriatal dopaminergic system, and more specifically, the intactness of the presynaptic dopaminergic terminals. Its availability may be limited to tertiary centres, and not all countries have access to DaTscans. Its usefulness in the investigation of a patient with parkinsonism is relatively limited, since it cannot differentiate between different forms of degenerative parkinsonism (ie, PD and progressive supranuclear palsy).1 Nonetheless, it can differentiate essential tremor from PD (for which it is licensed in Europe and the USA) and can also differentiate degenerative forms of parkinsonism from drug-induced parkinsonism (the latter presenting with a normal DaTscan).2 In our clinical practice, only a select group of patients receives a DaTscan, usually younger patients with …