There are considerable data to indicate that psychotic depression is not just a severe form of depression but a distinct form of depression. Mostly in terms of clinical symptoms, course, biology, treatment response and outcomes. However, not every difference is indisputable, there are inconsistencies among studies and these differences might not be strong enough to be used in diagnosis.
Differences in clinical symptoms
1. Unusual thought content, increased feelings of guilt and psychomotor disturbances such as agitation and retardation are the most robust differences compared to non psychotic depression for clinical symptoms.
2. Early onset psychotic depression has been associated with a likely bipolar course.
3. The greatest cognitive impairments of psychotic depressed patients compared to nonpsychotic major depression were: verbal memory, executive functioning and psychomotor speed. An issue that remains is the medication use of psychotic depressed patients. Usually they are on more different drugs than the nonpsychotic depressed, especially antipsychotic which can influence the test scores.
4. Psychotic depressed patients have higher rates of nonsuppression on the dexamethason suppresion test (64%) compared to nonpsychotic depressed patients (41%). The sensitivity and specificity are not high enough to use these tests routinely for diagnosis.
5. ECT is very effective in the acute phase of the treatment of psychotic depressed patients. The data are unclear regarding the duration of this effect.
Issues involved with the distinction between the two types of depression:
1. What is called psychotic depression, hallucinations and delusions, and what kind of delusions, only mood congruent delusions? In Europe the presence of mood congruent delusions and hallucinations justifies the diagnosis psychotic depression. Should we look at dimensions of psychosis instead of a binary division?
2. In the DSM IV psychotic depression is linked to severity of the depression. The relationship between severity and psychotic features is not that strong. This implies a scale for severity and a separate classification for psychotic features.
3. The authors of the article promote a separate dimension for psychotic features with the loss of the distinction between mood congruent and mood incongruent delusions. A development not encouraged by Dr Shock.
4. Additionally more research is needed for the distinction between psychotic depression and schizoaffective disorder.
J. Keller, A. F. Schatzberg, M. Maj (2007). Current Issues in the Classification of Psychotic Major Depression Schizophrenia Bulletin, 33 (4), 877-885 DOI: 10.1093/schbul/sbm065