If you like my research updates but need a break from the molecular stuff, here’s an interesting and unexpected clinical discovery, usable at routine visits for care of PSP.
Michelle Troche, PhD, is a speech/language specialist in the Laboratory for the Study of Upper Airway Dysfunction in the Department of Biobehavioral Sciences at Columbia University’s Teachers College. She’s a past grantee of CurePSP’s
for a project published a year ago on training patients with PSP to protect their airways from aspiration. Now, she and her team, with James Borders as first author, have analyzed cough function in quantitative detail in patients with PSP and Parkinson’s.
The two groups of 26 patients were designed to be similar in terms of age, sex, disease duration and severity of swallowing difficulty. Their cough was analyzed with a device called a pneumotachograph (“air-speed-writer’) that fed the data into a software system. The procedure was performed during both coughing on request and coughing induced by a 2-second spray of capsaicin in 4 progressively increasing concentrations. Capsaicin is an irritant found in hot peppers, so kudos to those volunteer patients!
After a sophisticated statistical correction for confounding factors, some results were as expected: that the patients with PSP were able to generate only a fraction of the expiratory flow rate and volume of those with PD. However, another result was unexpected: patients with PSP were more bothered by increasing concentrations of the capsaicin than were those with PD, but were no more likely to respond by coughing.
In the researchers’ words, “. . . it is interesting to note that although both groups exhibited blunted urge-to-cough slopes compared to prior research in healthy adults, patients with PSP demonstrated increased urge to cough compared to PD. This means that even though the participants with PSP were perceiving the increasing cough stimulus more than patients with PD, they were not coughing more to that stimulus.“
So what does this mean? We think of PSP as a motor and cognitive disorder, but this result shows that there’s also a sensory deficit. The sensory input into the cough reflex takes place in the brainstem, the main location of pathology in PSP, so this result makes sense. It’s just that no one had previously thought about it. (The same phenomenon accompanies many important scientific discoveries – they seem so obvious in retrospect.)
Another brainstem reflex, the auditory startle response, has long been known to be impaired in PSP but not in PD, so the results of Borders et al have that ex ante confirmation.
Like any pioneering work, this one has its limitations. Although the PSP and PD groups were similar in terms of disease duration (both about 5 years) and swallowing function, the PSP group was much worse in terms of overall disability as measured by the widely-accepted Schwab and England Activities of Daily Living (SEADL) scale. With 100 being normal on the SEADL, the PSP group averaged 48, the PD group 79. This is expected given PSP’s more rapid disease course from onset to death — the 5-year disease duration is a far greater fraction of the average survival in PSP (7 years) than in PD (15 years). So perhaps the authors should/can add the SEADL score to their statistical model. Another issue is that the experimental procedure did not consider any effect on the cough function of PD medication, which dramatically helps general motor function of PD but not of PSP.
Now, how can we use this information? Dr. Troche and colleagues suggest that patients with PSP be monitored closely for cough deficit and that their own, previously published protocol for sensorimotor training in PSP, referred to above, could be instituted sooner rather than later.