Occam's razor and Hickam's dictum: a dermatologic perspective.

Diagnostic heuristics help ease the cognitive load in our day-to-day work. Occam's razor or the rule of diagnostic parsimony is a diagnostic heuristic often applied in dermatology. Occam's razor dictates that all things being equal, one diagnosis (as opposed to several diagnoses) should be sought to explain a patient's presentation. While this can often be helpful, it can also obscure the full picture. Hickam's dictum is an aphorism expressing the opposite opinion: "patients can have as many diseases as they damn (or darn) well please." This acknowledges that multiple simultaneous processes can be at play. This article delves into the implications of use of these approaches and offers tips through cases illustrating the limitations of Occam's razor and when Hickam's Dictum should be invoked.