A differential diagnosis should be placed in the case records in a prominent place, with a clear indication of who made it ('diagnosis' will be used in this section because of current conventions, but the difference between identifying a disorder and inferring an underlying diagnosis already noted must be kept in mind). When the patient suffers from more than one disorder it is usually possible to select one as the main diagnosis and specify the other(s) as additional or subsidiary diagnoses. The main diagnosis will usually be the one that is leading to immediate action, but the choice may depend upon the purposes for which the diagnoses are being recorded. Usually it reflects the reason for the current contact with services or admission but there are patients and occasions when, for instance, it makes more sense to record a lifetime diagnosis (such as schizophrenia or bipolar disorder) as the main diagnosis, even though something else such as anxiety or a phobic disorder is the reason for the current episode of care.
When one main diagnosis clearly applies yet does not account for some symptoms which, although a significant part of the clinical picture, still fall short of fulfilling the criteria for another disorder, it is useful to record these simply as 'additional symptoms' (for instance, depressive disorder with some obsessional symptoms; agoraphobia with some depressive symptoms, etc.). Neither ICD-10 nor DSM-IV mention this way of recording symptoms 'left over' after the main disorder has been accounted for, even though it is a useful clinical custom familiar to many generations of clinicians in a variety of countries. However, omission from formal classifications should not be allowed to inhibit clinicians from following clinical habits they find useful.
When there is reasonable debate about what is the best diagnosis out of two or more possibilities, one must be chosen provisionally as the main diagnosis as a basis for action but the other should be recorded as an alternative diagnosis. It is also good practice in quite early stages of the assessment process to record provisional diagnoses, which can then be changed as more information becomes available. About a third of psychiatric patients fulfil the criteria for more than one disorder as defined in current classifications, but as already noted, this does not carry the same implications about underlying morbid physiological, psychological, or anatomical processes as would a statement about the presence of the same number of medical or surgical diagnoses.
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