Are doctors medical detectives?

An eye for detail

Such subtleties lead doctors towards diagnoses, too. Pitted nails (these look like the surface of a thimble) are sometimes seen in psoriasis, for example. Mees’ lines (transverse white bands across the nails) are associated with arsenic poisoning, heart failure, renal disease and chronic infections.

Absence is as telling as presence. Mrs Agwu’s right leg is not weak – this likely excludes a stroke (another explanation for a scuffed shoe). In ‘Silver Blaze’, Holmes notes the curious incident of the dog in the night-time: the dog did not bark, thus it must have recognised a shady midnight visitor. 

It’s tempting at this juncture to rush towards a conclusion, but Holmes guards against this: “It is a capital mistake to theorise before you have all the evidence.” If a letter from Mrs Agwu’s GP outlined her slowing down and blank expression, I might consider a diagnosis of depression, testing this hypothesis by asking questions about her mood.

There’s danger in this hypothetico-deductive approach, akin to the crime of Procrustes – the inclination to fit the facts to our opinions instead of our opinions to the facts (Procrustes was a figure from Greek mythology who offered unwitting travellers a bed for the night. Little did they know he would stretch them or amputate their legs to fit the bed). In being welded to this possibility of depression in Mrs Agwu, I might miss the clues pointing towards her Parkinson’s.  

Holmes usually draws upon abduction rather than deduction: starting from observations or the known facts, then deriving their most likely explanation. Abduction entails working backwards to a probably or possible conclusion.

In ‘The Adventure of the Blue Carbuncle’, Holmes sees a cast-off hat and concludes that the man is highly intellectual (the hat is large – “a man with so large a brain must have something in it” – we now know this has no scientific basis, sadly) and experiencing a decline in fortunes and foresight indicating “some evil influence, probably drink”, since the expensive hat has entered a state of disrepair. 

Holmes reasons, from hairs on the hat’s lining, that the man is middle-aged, with recently cut, grizzled hair, which he anoints with lime-cream. “It is extremely improbable that he has gas laid on in his house,” he concludes, given the presence of tallow stains.

Admittedly, one recent critic described this hat trick as “barely a half-step from parody”. In my view, though, Holmes was no ordinary detective, just as Joseph Bell was no ordinary doctor.

Arguing backwards

This abductive approach is the most commonly used investigative logic used in real-life murder investigations and is also often used iteratively in medicine, where we argue backwards from symptoms (the effects) to disease (the cause). Here’s an example:

Premise 1: Most people with chronic untreated gout have tophi (crystals of uric acid, usually in or around joints).

Premise 2: This patient has tophi.

Conclusion: This patient probably has chronic untreated gout.

Observations made and reasons reasoned, it’s time to consider all potential causes or suspects before reaching a final conclusion (termed differential diagnosis in medicine). “One should always look for a possible alternative, and provide against it. It is the first rule of criminal investigation,” says Holmes. Inspector Stanley Hopkins is also schooled by Holmes, who tells him in ‘The Adventure of Black Peter’: “You were so absorbed in young Neligan that you could not spare a thought to Patrick Cairns, the true murderer of Peter Carey.”

Yet, for all these parallels, differences abound between the crime scene and clinic consultation. We regularly face messy contradictions and uncertainties that are absent from the Holmesian universe.  

“When you have eliminated the impossible, whatever remains, however improbable, must be the truth,” Holmes says, but in medicine, there is inevitably more than one improbable solution, and more than one that might be true. Two people with the very same disease might present with different symptoms. Two people with identical symptoms often have different disorders. Many disorders have yet to be elucidated.

Doctors also cannot work on logic alone. Hermeneutics matter – the interpretation of text: the stories of our patients, their lived experience of illness, and our diagnostic tools. So does semiotics – the doctrine of signs: the bull’s-eye rash of Lyme disease or the tiny Koplik spots of measles inside the mouth.

In some cases, the methods of doctors more clearly reflect those of other literary detectives, who go beyond the singular theory or neat resolution. The investigative approach of William of Baskerville (a Franciscan monk in Umberto Eco’s ‘The Name of the Rose’) seems more closely attuned to medical diagnosis, what with its multiple layers of reasoning and “complex of motives, coincidences, and perspectives”.  

But none of this should underplay the strong Holmesian parallels with medicine. I sense, as I examine Mrs Agwu in a hospital just a few miles from Baker Street, that there are more similarities than differences between Holmes’ detecting skills and our doctoring ones. That much, Holmes might say, is elementary.