“Patients can have as many diseases as they damn well please”
John Hickam, MD.
“Among competing hypotheses, the one with the fewest assumptions should be selected.”
William of Ockham (c. 1287–1347)
The clinical presentation may be indistinguishable
e.g. Acute pulmonary oedema versus Infective exacerbation of COAD
When the presence of a condition confounds the interpretation of a test for another condition
e.g. Chronically troponin elevation in a renal patient with acute chest pain
One condition may lead to worsening of another (or vice versa)
e.g. Anaemia secondary to GI blood loss causing angina
e.g. Acute mental disturbance leading to drug ingestion or drug ingestion leading to acute mental disturbance
The treatment of one condition may make the other condition worse
e.g. beta blockers for atrial fibrillation leading to brochospasm in asthmatics
The nature of one condition makes it difficult to comply with treatment of another
e.g. use of a walking frame for a sprained ankle whilst simultaneously sustaining a fractured wrist
e.g. taking medication with poor eyesight
The psychosocial situation makes treatment risky
e.g. IV antibiotics for cellulitis with hospital in the home in an active IV drug user
e.g. Outpatient treatment of hypomanic patient with moderately severe asthma exacerbation
Multiple possibilities with mutually contra-indicated treatments
e.g. unstable angina requiring heparin versus aortic dissection requiring rapid blood pressure control