Iterative diagnosis.

When is iterative diagnosis used? General practitioners will recognise that they often formulate one or more presumptive hypotheses as the patient walks into the room or when they start speaking: a “hang dog” demeanour suggests depression; a unilateral stiff arm gait suggests parkinsonism; the acute onset of vertigo when rolling over in bed suggests benign positional vertigo. The general practitioner then listens to the history through the “filter” of the initial hypothesis: does the patient describe low mood, agitation, sleep disturbance? Does he or she get stuck as they roll over in bed; have they noticed that the fingers of the non-swinging arm are clumsy; does the vertigo come on with head movement and become less severe over a minute or so? The general practitioner’s examination will usually be directed towards supporting or refuting a hypothesis: on direct questioning does the patient admit to anhedonia and pessimism? Does he have lead pipe rigidity of the arms? Does the Hallpike test have positive results? Sometimes intuition applies a brake to the reasoning in the recurrent (iterative) testing: despite the coherent illness narrative, something doesn’t fit. Although the doctor has seen a hundred febrile children with sore throat, something “just doesn’t feel right” about this one. This may prompt referral or early review.