American history is full of weird stuff, and some of that weirdness crops up long after the era or subject in question has passed. For proof, just look at all the diseases people have "diagnosed" Abraham Lincoln with.
Was old Honest Abe really all that honest about his health? Despite the fact that Lincoln’s actual cause of death was pretty clear-cut (conspiracy theories aside), the sheer amount of Abraham Lincoln health issues people have supposedly discovered posthumously almost leads one to believe that John Wilkes Booth was acting out of mercy. If everything that modern doctors or historians have claimed about the 16th President of the United States is true, he was riddled with illness. Everything from syphilis to constipation has been tossed out by armchair experts..
While some of the medical claims about Lincoln may hold water, they obviously can’t all be true. A diagnosis or two might feature actual research, but most of the speculation consists entirely of anecdotal guesswork, and that doesn’t have a reputation for accuracy. The real answers will never be known, which is probably part of the reason why theorizing about Abe's health (or lack thereof) is still so popular today.
Probably the most common diagnosis associated with Lincoln is Marfan Syndrome, a genetic disorder that affects one’s connective tissue. It’s easy to see why people might think Lincoln had it, as its victims are normally quite tall, thin, and long-limbed. Lincoln remains the tallest president ever at 6’4”, and was incredibly tall for his time period.
However, no testing of Lincoln’s remaining DNA samples has been conducted for Marfan. Detractors say his excellent cardiovascular health and vision give good evidence that he didn’t have it.
Could Lincoln have had syphilis? It was definitely around plenty back then, and Lincoln’s former law partner claims that he told him about his affliction. Lincoln could very well have had syphilis, but there isn’t much direct evidence of it. More incendiary accounts claim that Lincoln passed the disease onto his wife and children, resulting in early deaths for the children and eventual madness for Mary Todd, but this is speculative at best.
Lincoln did have smallpox at one point in his life. He is said to have contracted the disease right after he delivered his famous Gettysburg Address in 1863, but most thought it was a mild case.
Recent evidence suggests that the illness affected him more seriously than previously thought, and that it hampered him while in the White House. Some claim that Lincoln had to carefully choose which advisors he personally met with in order to avoid further complications.
The best "catch-all" diagnosis for Lincoln is probably Multiple Endocrine Neoplasia, type 2b. The disease, which carries the boy-band-like acronym of MEN2B, would explain Lincoln’s lanky body, weird lips, constipation, and hypotonia. It also increases a person’s risk of cancer, and there is a history of that in Lincoln’s family. Lincoln’s famous mole, his one drooping eye, and even his depression could all be interpreted as manifestations of MEN2B. No DNA testing has been done to confirm this theory, however.