Progressive supranuclear palsy

Progressive supranuclear palsy (PSP), also known as the Steele-Richardson-Olszewski syndrome, is a tauopathy and considered a neurodegenerative disease with no currently efficacious treatment. 

Epidemiology

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

Clinical presentation

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. 

Radiographic features

MRI

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
  • midbrain to pons area ratio (figure 1): reduced area ratio on the midline sagittal plane to approximately 0.12  (normal ~ 0.24) ⁴. Most accurate imaging feature which also helps to distinguish it from MSA-P (shows pontine and midbrain atrophy) 
  • 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) ^8,6
  • morning glory sign: loss of the lateral convex margin of the tegmentum of midbrain ⁷ 
• T2: diffuse high-signal lesions in
  • pontine tegmentum
  • tectum of the midbrain
  • inferior olivary nucleus

Nuclear medicine

On SPECT/CT with I-123 ioflupane, there is 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.

Differential diagnosis

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

• Parkinson disease
  • spares the midbrain and superior cerebellar peduncles
• multiple system atrophy (MSA)
  • predominantly affects middle cerebellar peduncles and pons (hot cross bun sign)
• corticobasal degeneration (CBD)
  • cortical atrophy prominent