Possible Causes
The unquestioned diagnosis at the time, and thereafter in countless references, was paralytic poliomyelitis, which was at the time widespread. One of the foremost polio experts, Dr. Lovett, made the diagnosis based on personal observations of the patient. Also, the disease struck in mid-summer, when poliomyelitis was more common. Furthermore, it has been reported that motor neurons innervating muscles vigorously exercised at the start of polio are those more likely to be paralyzed. Finally, fever usually occurs in polio.
Read more about this topic: Franklin D. Roosevelt's Paralytic Illness