The practice of ‘diagnosis by exclusion’ in rheumatology has resulted in over-testing and diagnostic error and goes against the principles of diagnostic reasoning, a group of US rheumatologists says.
Diagnosing by exclusion, a principle employed for several rheumatic diseases such as polymyalgia rheumatica, seronegative rheumatoid arthritis, fibromyalgia, and Behcet’s syndrome, is subjective and conditional, “which misaligns it with principles of diagnostic reasoning, resulting in unnecessary testing and premature closure,” Dr Michael Putman and colleagues from the Medical College of Wisconsin, write in an article published in Rheumatology.
They argue that in rheumatology there is no pre-specified list of all possible “exclusions”, noting that an exclusionary list for any rheumatic disease would result in “significant variation” as it would be subjective and dependent on “prior experience, cognitive dispositions, and physician biases” and a patient’s presentation.
And even if there were set exclusion lists, it would be impossible to determine the sensitivity and specificity of a rheumatologist deciding that a disease had been excluded, “because diagnostic tests have not been designed to function this way”.
“We can say with confidence that a negative test decreases the likelihood of ANCA vasculitis. We cannot say how that same test influences the likelihood of Behcet’s syndrome or sarcoidosis, because diagnostic testing has not been designed for a reductionist process,” the authors said.
“Diagnostic tests increase or decrease the probability of a disease for which the testing has been studied. Outside of this context, we are misapplying basic principles of diagnostic reasoning,” they added.
Instead, they advocate a probabilistic ‘Bayesian reasoning’ approach, which, they said, “requires a different – and ultimately more patient-centric – set of skills,” including “expertise in epidemiology and narrative medicine, which allow the diagnostician to formulate a pre-test probability that the person before them has a disease”.
“They include knowledge of the performance characteristics of physical examination findings and subsequent testing and an ability to use this knowledge to arrive at post-test probabilities. Most importantly, this perspective encourages rheumatologists to become proficient in communicating risk, embracing uncertainty, and considering alternative diagnoses,” they concluded.