What happens if we change the 9-items list to a 10-items list, but keeping the temporal presentation and the core symptoms (sadness and anhedonia) the same? Does this help to capture patients suffering from depression , that were otherwise missed? Does this affect treatment strategies?
First it depends on which 10th item was added. If it is a common symptom then the prevalence of depression would rise slightly. However it would not automatically increase the rate of detected depressions because undetection is generally not due to a failure to fulfil DSM criteria but rather a failure to 1. look for any relevant symptoms 2. failure to recognise symptoms are linked with depression (vs other non-specific causes) and 3. reluctance to apply a label of clinical depression. So the effect of adding a 10th item would be more visible when systematic screening is applied because each case could be matched against the symptom list. Also for the record ICD10 does include 10 items for depression and so does DSMIV/5 if one includes the loss of function/distress which is required for a diagnosis. That is its 9 symptoms+distress/dysfunction=10. So.....If you see a PHQ9 questionnaire without the function item, it is not following DSMIV/5 rules. Hope that helps
As Alex says, it makes a difference how common the "new" official symptom is. Equally more important is how strongly correlated it is with the existing symptoms. If everyone who "has" the new symptom already met 5+ of the existing criteria, it would make zero difference diagnostically. But to the extent that it contributed "unique" variance, the outcomes would be
(a) an increase in the reported prevalence of major depression (of which clueless journalists would make much)
(b) an increase in diagnostic sensitivity (i.e., more people "with" depression, assuming it is a "real" something, would be identified
(c) a decrease in diagnostic specificity (i.e., more people "without" depression would be mistakenly diagnosed as having the disorder
I believe including a 10th item would allow for more non-typical cases to be considered, the ones which have non-pathognomonic symptoms related to depression (this also depends on what the 10th item is). This may potentially hamper the differential diagnosis. With too many items, tools loose their flexibility and clinicians fail to see the variance.
The answer of Mary Canellopoulou is correct and an important alert. Non-typical cases are problematico for any categorial diagnostic system.
Now, I see from the answers that there would be a change, for good or for bad. How would such a change affect treatment approach? Given that this affects differential diagnosis, what happens to depression severity?
We would be treating depressed people who now go untreated, so they would be helped. We would also be treating non-depressed people who currently don't get treated, so they would be paying (money, side effects, and self-esteem/stigma) for unnecessary care.
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