PPS Spinal Cord Atrophy
Question: A February 2022 study claims that patients diagnosed with PPS have spinal cord “gray matter atrophy” in their necks and also have muscle weakness in their arms, hands and feet. Is spinal cord atrophy the cause of PPS?
Dr. Bruno’s Response: I read the study when it was published last month and didn't think it was worth mentioning. Only 20 polio survivors said to have PPS were studied and compared to non-polio survivors, not to polio survivors without PPS. It's no surprise that survivors were found to have spinal cord gray matter atrophy, that is damage to the "gray" spinal cord motor neurons ("polio" means gray in Greek).
This study of only 20 polio survivors links gray matter atrophy not only to post-polio muscle weakness, but also statistically performs multiple comparisons between gray matter atrophy and other factors, e.g., fatigue, pain, depression, age, sex, age at or time since polio.
Unfortunately, the statistics applied to draw these conclusions are incorrect, the authors themselves stating, "Given the exploratory nature of these...analyses in this rare disease, we report [statistics] explicitly not adjusted for multiple comparisons." More than 175 subjects would have been required for a valid statistical analysis and appropriate conclusions.
The editors of the journal who published the study of "this rare disease" (having 20 million survivors worldwide) should have required appropriate statistics or rejected the paper outright.
Source:
Spinal cord gray matter atrophy is associated with functional decline in post-polio syndrome
Wendebourg MJ, et al. Eur J Neurol. 2022 May;29(5):1435-1445. doi: 10.1111/ene.15261