Indeed, it is statistically more probable, especially in the ageing patient, that multiple yet independent disease processes occur to account for an unusual set of symptoms as opposed to a single ‘rare as hens' teeth’ diagnosis. It follows that if one is to adopt the principle of Saint's triad for a particular presentation, searching for a unifying cause for the given set of symptoms would be pointless. This is not a new notion many philosophers even dating from William of Ockham's time - such as Walter Chatton (c.1290-1343) felt - Ockham's philosophy too simplistic: ‘Consider an affirmative proposition, which, when it is verified, is verified only for things if three things do not suffice for verifying it, one has to posit a fourth, and so on in turn (for four things, or five, etc.)’ 6
5 Its relevance here lies in the fact that since there is no pathophysiological basis for the co-existence of these three maladies, it is possible for multiple pathologies to co-exist but first manifest together in a single presentation. This describes a specific surgical presentation consisting of gallstones, hiatus hernia and colonic diverticulosis. Thus, there exists a converse, or ‘anti-razor’ to Ockham's, known as ‘Saint's triad’. Thus it conforms to Ockham's razor in just the way that House's two separate diagnoses do not.īeing a fit young 19-year-old is one thing, but as we grow older, many varied symptoms may simply be a reflection of many varied and co-existing pathologies. The side effects of the colchichine caused the clinical features unaccounted for by the upper respiratory tract viral infection and so the story becomes complete.Įven though this all seems a little far-fetched at first glance, it is still the simplest and most unifying explanation available. Therefore, the components that comprised this strange presentation were actually very simple a man with a cough took the wrong tablets by mistake. As the story unfolds, it becomes evident that the man had been self-medicating for a pre-existing viral cough but a pharmacy error had caused an accidental swap between the similar-looking colchicine and his cough medication. Thus the single set of symptoms in this otherwise fit and well man have been met by the rather intellectually lazy pitch of two distinct diagnoses. 4 The eponymous consultant cannot fit the clinical picture together and initially diagnoses two unrelated conditions: a sinus infection and hypothyroidism. In a 2004 episode of the popular US medical drama, House, M.D., a 19-year-old male collapses and presents to hospital with a rather incongruous set of clinical features: hypotension, nausea, a dry cough, abdominal pain and leucopenia. It is perhaps most eloquently described in Samuel Shem's famous semi-autobiographical novel The House of God, ‘When you hear the beats of hooves, think horses, not zebras’. 2 More recently, the principle has spawned a number of nominal variations including the ‘principle of simplicity’ and the ‘KISS principle’ (Keep It Simple, Stupid). However, Ockham's razor offers us a single diagnosis that fully accounts for this single presentation and guides us to a diagnosis of meningitis - the explanation that requires the fewest number of assumptions.įor centuries, Ockham's razor has proved to be an effective tool for weeding out unfavourable hypotheses and scientists use it every day even when they do not cite it explicitly. Imagine a patient presents to casualty complaining of headache, neck stiffness, fever, and confusion - it is of course perfectly possible that he simultaneously developed a subarachnoid haemorrhage, torticollis, and hepatic encephalopathy. The principle, Numquam ponenda est pluralitas sine necessitate, has over the years been interpreted in a number of ways but is perhaps best translated as ‘Plurality ought never be posed without necessity’- that is, the simplest and most unifying explanation for any given problem is the one most likely to be correct the idea being that other, less satisfactory, explanations are ‘shaven off’ in the process. 1 William of Ockham, its creator, was a Franciscan monk in the early 14th century who studied Theology at the Universities of Oxford and Paris. How should the physician react to these challenges in order to correctly diagnose and optimally treat the patient? This article began by stating the principle of parsimony, better known as ‘ Ockham's razor’, (also spelt ‘Occam’).
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