Some prognostic help

Sooner or later, most patients with PSP or someone they rely on will ask the doctor, “What’s going to happen next, and when?”  Until now, that question has only been answerable by saying, “Well, the symptoms you have now will slowly get worse and you may develop some additional ones.” or “I don’t know; everyone’s different.”  If the question is, “How long will I survive?” the only available answer has been to quote the published averages for PSP, which have a wide variance. All too often, the answer is, “Don’t worry about that — just take it one day at a time.”

A long-gestating project of mine has finally seen the light of day.  It uses scores on my patients’ PSP Rating Scale (PSPRS) scores gathered from 1995 to 2016 to allow clinicians to predict how much longer it will take for a given patient to reach certain disability milestones and death.  It also proposes a new five-point clinical staging system that we used as some of the disease milestones.  It appears in the August 2020 issue of Movement Disorders Clinical Practice and is available here.

Assisting in the effort was my trusty statistician, Pam Ohman-Strickland, of the Rutgers School of Public Health.  She was also my co-author in the original validation of the PSPRS in 2007.  BTW, if you want to read that paper, here’s your chance. Since then I’ve refined the rules and instructions for administering the PSPRS and that’s available here.

Two undergrads helped out in the new project: Emily Beisser did most of the analysis for the new staging system and Francesca Elghoul helped with data wrangling.

The outcome milestones number 13 in total.  The first seven are severe difficulty with swallowing solids, swallowing liquids, speech, eye movement, general movement, balance and thinking. For each, “severe” is defined as exceeding a specific score on the relevant PSP Rating Scale item(s).  The next five are the stages on the proposed “PSP Staging System” and the last milestone is death.  

We created the five PSP stages by totaling four of the 28 items on the PSPRS: swallowing solids, swallowing liquids, gait, and the ability to return to one’s seat safely from a few steps away without using the hands.  They’re items 3, 13, 26 and 28 on the PSPRS.  The point total for those four items, each rated 0 to 4, are divided into five groups: 0 points, 1-4, 5-8, 9-12, 13-15 and the full 16.  Although this staging rubric uses only two of the many possible deficit areas in PSP, we found that the total of these those four items correlates very closely with the total PSP Rating score.  We chose swallowing and gait/balance as candidates because so many of the serious complications and disabilities of PSP lie in those areas. I’ll devote a future post to the issue of “stages” in PSP.

Tables 3 and 4 in the new paper show the meat of the matter.  You’ll see that the input data are gender, the total PSP Rating Scale score at the time of the visit, and the rate of progression to date.  The last one has to be calculated by dividing the current PSPRS score by the number of months since the onset of the first PSP symptom.

Just a quick caveat: Please don’t try this at home. Many of the exam items on the PSPRS require training and experience to administer correctly; the scale and its instructions are in technical language; and the dating of the onset of PSP symptoms may not be interpreted by the patient or family as an experienced neurologist would.

I hope that these new results, to quote myself from the paper’s introduction, “may influence decisions to retire from work, hire caregivers, alter the home environment, move to a seniors-oriented or institutional living arrangement, decide on a feeding gastrostomy and not least, prepare psychologically for advanced disability and death.”  Until we have a way to prevent or halt the progression of PSP, this will be an important part of how clinicians can help their patients.