The clinical case report: a tool for hypothesis generation.

The clinical case report is generally limited to a description of unusual examples of the complications of disease or responses to therapy. However, it can also be used to present novel hypotheses which have been derived from individual cases. Two examples of this latter genre are presented and updated. These are Syndrome X and the stiff left atrial syndrome. In both instances, general and novel formulations were derived from single cases. With respect to Syndrome X, a hypothesis was generated that the chest pain and ST abnormalities in these patients represent excess activation of adenosine A1 receptors in the absence of myocardial ischemia. With respect to the stiff left atrial syndrome, recognition of the first case led to the recognition of the problem in many others. Now, a variant of the syndrome has been recognized in which mitral regurgitation is also present. In addition, the possibility that tricuspid annuloplasty may rescue patients dying of cardiac cachexia due to right heart failure caused by combined pressure and volume overload of the right ventricle is outlined.