Not Your Father’s PSP

As it turns out, PSP comes in many clinical flavors. Back in the 80s I remember some patients whose illness looked like Parkinson’s until I realized that they weren’t responding to my levodopa prescriptions, at which point I repeated a careful ocular motor exam and found square wave jerks and slow downward saccades. I also remember one member of my first series of 41 patients with PSP from 1988 with severe gait apraxia and freezing as his most disabling feature.
Then, in 2005, David Williams and colleagues, mentored by Andrew Lees at Queen Square, published what is probably the most important clinical paper on PSP in the half-century since Steele, Richardson and Olszewski. That work delineated and named PSP-Richardson syndrome (PSP-RS ) and PSP-parkinsonism (PSP-P). This wasn’t just a new way to slice a clinical spectrum sharing the same basic pathology; the two variants actually had statistical differences by cluster analysis. This suggests that they differ at the pathoanatomic level. They even differed in the ratio of 4R/3R tau. (It turns out that the predilection of PSP’s tangles for 4R tau is driven by RS.)

Since then, a cornucopia of low-frequency clinical variants meeting pathoanatomic criteria for PSP has been described. In approximate descending order of prevalence after RS and PSP-P are corticobasal syndrome, postural Instability, pure akinesia with gait freezing, frontotemporal dementia, ocular motor predominance, progressive non-fluent aphasia, semantic dementia, and a cerebellar variant.
The clinicopathologic studies are only starting to appear, but it’s likely that they will all turn out to emphasize different cells, nuclei and brain regions. We will also probably see some subtle molecular differences among them (presaged by the 4R/3R difference between RS and PSP-P).

That sounds like different diseases to me. Different diseases shouldn’t be combined in treatment trials, genetic analyses or descriptive studies. What a mess.

Or is it? Maybe we don’t need to find causes and cures for each PSP variant individually. As they’re all tau aggregation disorders, maybe they will all yield to the same prevention. Maybe the mechanism of prion-like spread, by now pretty much a textbook verity, will apply not only to all of the “pure tauopathies” (and it’s not yet clear that all of the PSP variants are in fact pure tauopathies) but to all of the protein-aggregation-based neurodegenerative disorders. If it does, then poisoning that process could be the grand unified answer to Alzheimer’s, Parkinson’s, ALS, and PSP in all its malign variety.

3 thoughts on “Not Your Father’s PSP

  1. Thank you so much for sharing insight into this horrible disease, Dr. Golbe.

    Are there clinical differences between familial PSP and sporadic PSP? Do you think the same treatments and cures will likely benefit both once developed?

    • John:
      Thanks for this pertinent question. First of all, familial PSP is very rare. The best study of the issue found that the presence of a case of PSP among relatives of patients with PSP was barely higher than among relatives of healthy people. There appear to be no differences between PSP occurring with and without other PSP in the family. The autosomal dominant mutations in the tau gene that cause “familial PSP” actually cause a form of frontotemporal dementia.
      Once a prevention, treatment or cure for PSP is found, it’s just as likely to work for familial PSP as for sporadic PSP. The only caveat is the unlikely possibility that the treatment targets the “upstream” cause of the disease (i.e. a genetic mutation) rather than targeting a more “downstream” step in the disease-causing process.

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