A very long but fascinating article at Oxford Journals called:
Diseased, demented, depressed: serious illness in Heads of State
The author is The Rt Hon Lord David Owen. Lord Owen is a former British Foreign Secretary with medical training so he is in a unique position to give first hand opinions on what ailments various world leaders had.
He concludes by stating:
On balance, I believe there should be provisions in place in a democracy to ensure that before voting any candidate for Head of State or Government into office, whether for the first or for subsequent elections, the general electorate should know the results of an up-to-date independent medical examination. Relying on a politician, ambitious for office, to reveal their true health or on their own personal doctor, family or friends is not sufficient.