Progressive supranuclear palsy

Last revised by Calum Worsley on 31 Aug 2022

Progressive supranuclear palsy (PSP), also known as the Steele-Richardson-Olszewski syndrome, comprises a group of related tauopathies and considered a neurodegenerative disease with no currently efficacious treatment. 

Progressive supranuclear palsy typically becomes clinically apparent in the 6th decade of life and progresses to death usually within a decade (2-17 years from diagnosis).

Progressive supranuclear palsy is characterized by decreased cognition, abnormal eye movements (supranuclear vertical gaze palsy), postural instability and falls, as well as parkinsonian features and speech disturbances 1-3

It can be divided into a variety of subtypes many of which overlap with other neurodegenerative diseases that share an abnormal accumulation of tau proteins (discussed in the article on tauopathies9,10

  • classic
    • PSP-Richardson syndrome
  • brainstem variants
    • PSP-predominant parkinsonism (PSP-P)
    • PSP-pure akinesia with gait freezing (PSP-PAGF)
  • cortical variant
    • PSP-corticobasal syndrome (PSP-CBS)
    • PSP-behavioral variant of frontotemporal dementia (PSP-bvFTD)
    • PSP-progressive non-fluent aphasia (PSP-PNFA) 

Although certain features help in favoring PSP over alternative clinical diagnoses (Parkinson disease and multiple system atrophy for example) it should be noted that except in classical cases, imaging features can usually at most be suggestive of the diagnosis rather than pathognomonic, as there is overlap with other conditions. MRI features include 1-4:

  • midbrain atrophy
    • a useful imaging biomarker in classic and brainstem variants PSP 10
      • MR Parkinsonism Index (MRPI)
      • midbrain to pons area ratio (figure 1): reduced area ratio on the midline sagittal plane to approximately 0.12 (normal ~ 0.24) 4
      • midbrain to pons width ratio: reduced on the midline sagittal plane to <0.52 13
      • midbrain width: reduced on the midline sagittal plane to <9.35 mm 13
      • hummingbird sign also known as the penguin sign (case 1 and 2): the key is a flattening or concave outline to the superior aspect of the midbrain which should be upwardly convex 5,8
      • Mickey Mouse appearance (case 3): reduction of anteroposterior midline midbrain diameter, at the level of the superior colliculi on axial imaging (from interpeduncular fossa to the intercollicular groove: <12 mm) 6,8
      • morning glory sign: loss of the lateral convex margin of the tegmentum of midbrain 7
  • T2: diffuse high-signal lesions in
  • I-123 ioflupane SPECT: dopamine active transporter imaging shows loss of the normal comma- or crescent-shaped tracer uptake in the striatum. Instead, a period- or oval-shaped uptake is seen within the caudate nucleus head without tracer uptake in the putamen; quantitative assessment reveals reduced uptake in the putamen compared to norms
  • F-18 FDG PET: frontal lobe and/or midbrain hypometabolism support the diagnosis 11; the frontal areas particularly involved are the premotor, precentral, and prefrontal regions and anterior cingulate 11

Currently, treatment is aimed at symptoms. For example, in patients with primarily parkinsonian symptoms, medical therapy is typically levodopa combined with a dopa decarboxylase inhibitor (e.g., carbidopa) 12

Clinically it can be challenging to distinguish PSP from other entities especially when features are not typical 1,3

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Cases and figures

  • Figure 1: sagittal midbrain to pons ratio
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  • Case 1: hummingbird sign
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  • Case 2: hummingbird sign
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  • Case 3: mickey mouse sign
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  • Case 4: hummingbird sign
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  • Case 5: hummingbird sign
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  • Case 6
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  • Case 7: mickey mouse sign
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  • Case 8
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  • Case 9
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