Table 1.

Distinguishing features of Parkinson’s disease versus progressive supranuclear palsy and multiple systems atrophy

	Parkinson’s disease	Progressive supranuclear palsy	Multiple systems atrophy
Diffusivity	Variable changes reported in striatum and thalamus, most studies report no difference from controls	Increased in midbrain, basal ganglia, thalamus, cortex	Increased in striatum and middle cerebellar peduncles
Changes seen on routine clinical imaging sequences	··	Midbrain atrophy: “hummingbird” or “penguin” sign; atrophy of superior cerebellar peduncle	Hypointense putamen with hyperintense rim; loss of pontocerebellar fibres (“hot-cross bun” sign)
Other special sequences	Magnetisation transfer ratio and fractional anisotropy decreased, iron load increased in substantia nigra	Magnetisation transfer ratio decreased in striatum, globus pallidus, substantia nigra, and white matter	Magnetisation transfer ratio decreased in putamen, globus pallidus, and substantia nigra; iron sensitive sequences (relaxometry, phase-contrast susceptibility) show increased deposition in putamen
PET or SPECT: presynaptic dopamine tracers	All decreased, affecting caudal more than rostral striatum	All decreased, but rostral-caudal gradient might be lost	All decreased, rostral-caudal gradient is variable
PET or SPECT: striatal dopamine receptors	D2 binding increased in putamen in untreated patients, could normalise on therapy; might see slight reduction in caudate on prolonged dopaminergic therapy	D2 binding reduced	D2 binding reduced
PET or SPECT: glucose metabolism or cerebral blood flow	Increased in basal ganglia and cerebellum, decreased in premotor and posterior parietal cortex	Reduced in brainstem and medial frontal cortex	Reduced in putamen and cerebellum

SPECT=single photon emission CT.