The symptom profiles and severity patterns of PMD patients in the current outpatient sample were largely consistent with those reported in past research using more acutely ill hospitalized samples. PMD patients were more likely to endorse symptoms such as weight loss, insomnia, psychomotor agitation, indecisiveness, and suicidality compared to NMD patients. Furthermore, the severity of a number of depressive symptoms was greater in PMD patients, including depressed mood, appetite loss, insomnia, psychomotor disturbances (agitation and retardation), fatigue, worthlessness, guilt, cognitive disturbances (concentration and indecisiveness), hopelessness, and suicidal ideation. Many previous studies in this area failed to adequately account for other symptoms present when reporting differences among PMD and NMD patients, or to include a comprehensive analysis of the presence and severity of the full range of DSM-IV-TR symptoms of major depression. Results reflecting the greater frequency and severity of certain depressive symptoms in PMD patients were not completely surprising as the disorder is defined in part by its higher severity. However, several of the differences found among PMD and NMD patients remained significant even after controlling for demographic characteristics, symptom severity, and other non-depressive symptoms present. For example, PMD remained significantly associated with higher rates of insomnia, psychomotor agitation, indecisiveness, and suicidality even after controlling for other potentially confounding variables. In addition, PMD patients continued to show more severe levels of depressed mood, insomnia, indecisiveness, and suicidal ideation.
The current study provides useful information that could help to improve the identification and treatment of PMD patients in community treatment settings. Our findings were consistent with those of past studies suggesting that psychotic features may be sufficient but not necessary for identifying PMD. In a series of studies, Parker and colleagues also found that certain depressive symptoms, in addition to psychotic features, could be useful for discriminating among NMD and PMD patients. In one such study, PMD patients were more likely than NMD patients to evidence psychomotor disturbance, certain negative cognitions, the absence of diurnal variation, and constipation [17
]. A follow-up study found a similar pattern in PMD patients, including psychomotor disturbance, “morbid” cognitions (e.g., guilt and sinfulness), constipation, terminal insomnia, and appetite/weight loss [34
]. Furthermore, this general profile was confirmed in a PMD geriatric sample [35
]. Based on this work, Parker [36
] proposed a hierarchical classification system that views PMD as a modified form of melancholic depression typified by both delusions/hallucinations and severe psychomotor disturbance. The current study added to this previous work by addressing the severity of depressive symptoms in addition to their presence or absence alone, and showed that PMD is associated with more severe depressed mood, insomnia, indecisiveness, and suicidal ideation even after controlling for other symptoms. Given the frequent difficulty clinicians have diagnosing PMD due to patient underreporting or the presence of subtle psychotic symptoms, results from the current study and previous research suggest that symptoms such as psychomotor disturbance, insomnia, appetite/weight loss, cognitive disturbances, suicidality, and depressively distorted cognitions focusing on guilt or morbid themes should raise suspicion about the possible presence of PMD. In such cases, a more comprehensive assessment of psychotic features would be warranted.
Furthermore, understanding the frequency and severity of non-psychotic depressive symptoms in PMD patients could also prove useful in its treatment. PMD is often associated with treatment-resistance [10
], and tends to respond poorly to conventional treatment with antidepressant medications [9
]. Although the combination of selective serotonin reuptake inhibitors and atypical antipsychotic medications is increasingly seen as the frontline treatment for PMD, the superiority of this combined strategy over monotherapy with antidepressants has been questioned recently [37
], and more research in this area is needed. In light of the current findings, the treatment of PMD may be able to be improved by the use of medications that target specific aspects of the illness in addition to the psychotic features themselves, including psychomotor disturbance, appetite, and cognitive impairment. For more severe forms of nonpsychotic depression, combined treatment with medications and a psychosocial intervention has been shown to produce a modest improvement in outcomes over either treatment alone [38
]. Although psychosocial treatment development for PMD is still in its infancy [40
], it is possible that targeted psychotherapies that focus on improving treatment adherence and engagement (a frequent problem in this population), and decreasing suicidality, distorted thinking patterns, and functional impairment may be useful when used as an adjunct to medications [41
]. Tailoring treatment strategies (both pharmacological and psychosocial) to the specific symptoms of PMD patients may ultimately be needed to produce the most effective, feasible, and acceptable treatments for this population.
As discussed, the current study had several strengths, including the use of a large community outpatient sample, valid and reliable diagnostic assessments administered by trained interviewers, and comprehensive measures of DSM-IV-TR symptom criteria for major depression. However, limitations should also be considered. First, the number of PMD patients was relatively small, and our sample was low in ethnic/racial minority representation. Future attempts should be made to investigate symptom profiles in non-White patients due to potential differences in their clinical presentation of PMD. Given the broader literature showing racial/ethnic differences in primary psychotic disorders, the potential role of culture in the presentation and interpretation of PMD symptoms requires further investigation [42
]. Second, assessments were based mainly on patient self-report, and it would be useful to corroborate symptom reporting using observational measures or collateral interviews from family members or significant others. Third, the current results may not hold true for all patients experiencing PMD given our use of a treatment-seeking sample. Fourth, more acutely ill patients may not have been willing or able to participate in the comprehensive assessment. Finally, it is important to note that we did not assess all DSM-IV-TR symptom criteria for melancholic depression (e.g., distinct quality of depressed mood, lack of reactivity to usually pleasurable stimuli) because this section of the SCID was not administered. Future studies should more fully assess the relationship between this depression subtype and PMD.
Furthermore, certain characteristics of our sample may be important in the interpretation of results. The presence of hallucinations was more frequently endorsed in our sample than delusions. Past research, particularly on inpatients, has been conducted on PMD patients exhibiting delusions more frequently. Further research is needed to clarify whether there are clinical differences among PMD patients exhibiting different types of psychotic features. Additionally, the prevalence rates of PMD overall in the current sample is somewhat lower than those reported in the extant literature [11
]. Several factors may account for this: 1) the highest rates of PMD typically have been reported in inpatient or elderly samples; 2) patients with PMD may be less likely to seek treatment in outpatient settings; 3) our use of comprehensive diagnostic assessments may have improved differential diagnosis of PMD versus other disorders; and 4) the lower prevalence rate may be related to the particular characteristics of the clinic, which predominantly treats those with medical insurance (including Medicare). Finally, it is important to note that currently PMD is considered a subtype of major depression in the DSM, and it is unclear whether these patients represent a true nosologically distinct group, as some have argued [43
In conclusion, patients with PMD could be differentiated from those with NMD based the presence and severity of several depressive symptoms in addition to psychotic features. Symptoms including psychomotor disturbance, insomnia, indecisiveness, and suicidal ideation remained predictive even after controlling for the effects of illness severity and other factors. These findings are consistent with past research suggesting that PMD is characterized by a unique symptom profile, psychotic features, and higher levels of overall depression severity. The identification of specific depressive symptoms in addition to delusions/hallucinations that can differentiate PMD versus NMD can aid in the early detection of the illness, and also provide insights into potentially fruitful targets of treatment for this high-risk population.