Extremely rare. This is an extremely rare prion disease and diagnosis is based upon pathologic testing and physical exam findings may vary. The only reference to pinpoint pupils I could find stated that both were pinpoint, not just one. Here's a good article: http://www. Ncbi. Nlm. Nih. Gov/pmc/articles/pmid/17406189/ and http://www. Ncbi. Nlm. Nih. Gov/pmc/articles/pmc3214133/.