One of my favorite Charlie Munger quotes goes something like this:
"Warren, over the years you and I have appreciated the great value in learning from mistakes; Another thing we realized is that it's a lot more pleasurable to learn from other people's mistakes."
In light of that sage advice, here's another recent case report invoking Hickam's dictum. In this case, a 38-year-old man from Pakistan who has sex with men presents with uveitis and a rash on his palms and soles. He has a positive interferon-gamma release assay. This caused diagnostic confusion which resulted in the unnecessary invocation of Hickam's dictum. There is, after all, a simple explanation for the two findings, as I explicated in an online comment:
"This is an interesting case. Neither Ockham's razor, nor
Hickam's dictum, nor Crabtree’s bludgeon need be invoked to sort it out.
The annual incidence of syphilis in men who have sex with
men in the USA is a whopping 309 cases per 100,000 persons per year - almost as
common as community acquired pneumonia in unselected adults. Compare that to
2.9 syphilis cases/100,000 person-years in men who have sex only with women. A
risk factor that increases the incidence of disease over 100-fold should point
even the novice diagnostician straight to the diagnosis. Combined with a rash
on the palms and soles? The diagnosis is all but made. Positive RPR? We’re
finished here! For guidance on using incidence/disease frequency as a surrogate
for disease probability, see: https://pubmed.ncbi.nlm.nih.gov/34854514/
Next, IGRA (e.g., quantiferon Gold) is NOT a diagnostic test
for active tuberculosis infection (indeed, active infection is a cause of false
negative IGRA), it is used clinically as a marker of prior tuberculosis
exposure. In Pakistan, the annual incidence of tuberculosis is 230 cases per
100,000 persons per year, so it is hardly surprising that this patient has a
positive quantiferon-gold. This is a red herring rather than an instantiation
of Hickam’s dictum. Likewise, the dermatologist consultation was a false
negative test for secondary syphilis. It is unbelievable that they attributed
this rash to psoriasis, but this highlights that we should not put too much
credence into any single piece of data or consultation if it flies in the face
of the totality of the evidence. Similarly, angiotensin converting enzyme (ACE)
levels are notoriously both insensitive and non-specific.
In the end, there is a simple unifying (and unsurprising)
diagnosis in this case: syphilitic rash and uveitis in a man who has sex with
men. For an explication of Ockhams razor and Hickams dictum (and the limits of
their inferential powers), see: https://pubmed.ncbi.nlm.nih.gov/39467949/
Interestingly, Hickam started in the Boston hospital system,
went to Emory, then to Duke, and finally to Indiana. Though not formally
specialty trained, he did pioneering work in ophthalmology research, as well as
cardiopulmonary research. An entire edition of the Archives of Internal
medicine was dedicated to him after his death by reprinting seven of his
original papers – the entire issue of the journal."
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