A mild case of Polio? Then, it was probably a mis-diagnosis. Now, everyone would assume that it was just spin.
The New York Times, with its customary accuracy, has some of his stats wrong--his lifetime total of home runs (not counting World Series games) was 493 (they have 494).
The original Pride of the Yankees movie about Lou Gehrig is worth seeing--no doubt it takes a few liberties with details but it does give you an idea of why he was loved so much by fans.