Diagnoses are only hypotheses or opinions and we must expect them to
be changed in a proportion of cases. We should help this process of
change by documenting in writing the ‘particular’ evidence for each
possible diagnosis so far (i.e. found in that ‘particular’ patient) and a
plan for that particular diagnosis [1]. This helps the writer to think
clearly and helps a reader who may have to take over.
Any one diagnosis may be very uncertain but a carefully documented
differential diagnosis will be more certain. A finding with a short
differential diagnosis that accounts for a high proportion of patients
(e.g. 99%) will be a helpful diagnostic lead in this context [1]. This
may be a symptom, sign or test result (or a combination based on some rule
or heuristic). It is a ‘red flag’ lead if it has some serious
differential diagnoses.
In order to show that one of the differential diagnoses of a lead is
more probable, the plan must be to look for another finding (perhaps after
waiting or treating) that is ‘likely’ to occur in at least one of the list
of differential diagnoses and is ‘unlikely’ to occur in at least one other
diagnosis. These two 'likelihoods' form a ‘differential’ likelihood ratio
[1]. A ‘plain’ likelihood ratio based on a sensitivity divided by the
corresponding false positive rate is difficult to use in differential
diagnosis and can be misleading; its proper place is in population
screening [1].
The aim of diagnosis is to supplement failing emotional, homeostatic
and reparative feed-back mechanisms, so monitoring and feed-back is an
inherent part of the diagnostic process, from primary through to intensive
care. The diagnostic process is finalised when no further action is
needed for the moment. Gold standard tests and formal treatment selection
criteria are the best available so far; they do not guarantee certainty of
outcome [1, 2].
I think that clinical reasoning will continue to be more unreliable
and wasteful than it needs to be until diagnostic impressions are always
backed up with 'particular' evidence in writing. The techniques to do so
quickly and easily are becoming available [1].
References
1. Llewelyn H, Ang AH, Lewis K, Abdullah A. (2009) The Oxford
Handbook of Clinical Diagnosis, 2nd edition. Oxford University Press,
Oxford.
2. Llewelyn D E H, Garcia-Puig, J. (2004) How different urinary
albumin excretion rates can predict progression to nephropathy and the
effect of treatment in hypertensive diabetics. JRAAS, 5; 141-5.
Rapid Response:
Putting clinical reasoning in writing
Diagnoses are only hypotheses or opinions and we must expect them to
be changed in a proportion of cases. We should help this process of
change by documenting in writing the ‘particular’ evidence for each
possible diagnosis so far (i.e. found in that ‘particular’ patient) and a
plan for that particular diagnosis [1]. This helps the writer to think
clearly and helps a reader who may have to take over.
Any one diagnosis may be very uncertain but a carefully documented
differential diagnosis will be more certain. A finding with a short
differential diagnosis that accounts for a high proportion of patients
(e.g. 99%) will be a helpful diagnostic lead in this context [1]. This
may be a symptom, sign or test result (or a combination based on some rule
or heuristic). It is a ‘red flag’ lead if it has some serious
differential diagnoses.
In order to show that one of the differential diagnoses of a lead is
more probable, the plan must be to look for another finding (perhaps after
waiting or treating) that is ‘likely’ to occur in at least one of the list
of differential diagnoses and is ‘unlikely’ to occur in at least one other
diagnosis. These two 'likelihoods' form a ‘differential’ likelihood ratio
[1]. A ‘plain’ likelihood ratio based on a sensitivity divided by the
corresponding false positive rate is difficult to use in differential
diagnosis and can be misleading; its proper place is in population
screening [1].
The aim of diagnosis is to supplement failing emotional, homeostatic
and reparative feed-back mechanisms, so monitoring and feed-back is an
inherent part of the diagnostic process, from primary through to intensive
care. The diagnostic process is finalised when no further action is
needed for the moment. Gold standard tests and formal treatment selection
criteria are the best available so far; they do not guarantee certainty of
outcome [1, 2].
I think that clinical reasoning will continue to be more unreliable
and wasteful than it needs to be until diagnostic impressions are always
backed up with 'particular' evidence in writing. The techniques to do so
quickly and easily are becoming available [1].
References
1. Llewelyn H, Ang AH, Lewis K, Abdullah A. (2009) The Oxford
Handbook of Clinical Diagnosis, 2nd edition. Oxford University Press,
Oxford.
2. Llewelyn D E H, Garcia-Puig, J. (2004) How different urinary
albumin excretion rates can predict progression to nephropathy and the
effect of treatment in hypertensive diabetics. JRAAS, 5; 141-5.
Competing interests:
None declared
Competing interests: No competing interests