Comprehensive diagnostic assessments indicated that PMD was present in 2.4% of the current treatment-seeking outpatient sample or 5.3% of those diagnosed with major depression specifically. PMD patients were found to differ on certain demographic variables, including race/ethnicity and educational attainment. Overall, PMD patients tended to be more severely ill currently, to have a worse past course of illness, and to show higher functional impairment and disability related to their illness. PMD patients also had higher rates of certain comorbid conditions, although no differences were found for family history of disorders. After controlling for a variety of demographic and clinical variables, race/ethnicity, education, current depression severity, global functioning, and depression chronicity remained significantly associated with diagnostic status.
Rates of PMD found in the current sample were somewhat lower than those reported in previous treatment-seeking samples 16–54%.
The lower rate of PMD was not completely unexpected as the highest rates of the disorder generally have been found in inpatients. However, the prevalence of PMD in the current sample was lower than that demonstrated in previous epidemiological studies, which have reported that between 15 and 19% of people with major depression have psychotic features.[1, 2]
There are several potential explanations for this discrepancy. First, the use of structured clinical interviews administered by trained diagnosticians in this study may have improved differential diagnosis of PMD patients, especially in comparison with the diagnostic methods employed in past large-scale epidemiological surveys.
Alternatively, it is possible that depressed patients with psychotic features are less likely to seek treatment in outpatient settings,
which may partially explain their higher prevalence in hospital samples. In addition, the lower PMD prevalence in our sample may have been the result of the particular characteristics of patients treated at the recruitment site. The psychiatry outpatient practice predominantly treats patients with medical insurance (including Medicare) on a fee-for-service basis. It is possible that PMD patients are disproportionately uninsured or underinsured. Moreover, the highest rates of PMD have been reported in elderly clinical samples. However,[41, 43]
the average age of patients with this diagnosis in this study was 37, and the clinic does not specialize in the treatment of geriatric patients.
The finding that significantly more PMD patients were members of racial/ethnic minorities is consistent with past epidemiological research showing a higher proportion of African American patients with PMD versus NMD.
In a previous report from this data set based on a smaller subsample of PMD patients (n
= 15), a significantly higher number of Hispanic compared to Caucasian patients were found to have a PMD diagnosis.
These results were extended in the current larger sample of PMD patients (n
= 60). Given the broader literature showing racial/ethnic differences in primary psychotic disorders, the potential role of culture in the presentation and interpretation of symptoms requires further investigation.
The lower proportion of minority patients in our sample could also account for the lower prevalence of PMD found. Furthermore, results demonstrated that PMD patients were less likely to have obtained a college degree. Serretti et al.
also found lower educational attainment in their sample of PMD patients. It is likely that these ethnic and educational differences sometimes found between PMD and NMD patients may be at least partly explained by differences in socioeconomic status, as shown by Johnson et al.
However, it should be noted that race/ethnicity remained significantly associated with diagnosis even after education level, which represents a proxy for socioeconomic status, was controlled for in analyses.
Consistent with past research[9, 11]
and as expected, PMD patients had greater overall depression severity. Although some studies have failed to find differences in the onset of illness,[1, 14]
PMD patients in this study had a significantly earlier age of depression onset compared with NMD patients. The finding that PMD patients had nearly four times greater odds than NMD patients of chronic depression was consistent with past research demonstrating that PMD patients tend to experience much longer depressive episodes.[21, 22]
Furthermore, past research has indicated that patients with PMD have higher levels of suicidal ideation
and are two to five times more likely to have a suicide attempt [1, 46]
compared to those with NMD. This is consistent with current results showing that PMD patients had significantly higher current suicidal ideation severity as well as over four times greater odds of having a past suicide attempt.
Goldberg and Harrow
reported that functional impairment in PMD patients contributed to poorer perceived quality of life. However, past comparisons of PMD and NMD patients on measures of psychosocial functioning have produced conflicting results. Some studies have reported that PMD patients possess greater functional impairment over long-term follow-up,[16, 46]
whereas others have failed to find functional differences over time in comparisons with NMD patients.
In this study, PMD patients had significantly poorer social functioning and were more likely to evidence chronic occupational impairment (i.e., greater than 1 year out of work due to psychiatric illness). These discrepant findings in the literature may be explained by the clinical characteristics of different PMD samples. For example,
recently failed to find greater psychosocial impairment in PMD compared with NMD patients currently hospitalized, most likely because of the overall high severity of illness observed in the sample and possible “ceiling effects” on these measures. The current outpatient sample had a greater heterogeneity of illness, which may have increased the ability to differentiate PMD and NMD patients on measures of functional impairment.
This study represents one of the most comprehensive and detailed examinations of psychiatric comorbidity in PMD patients that has been reported in the literature to date. Patterns of comorbidity found in the current PMD sample, including the higher rates of anxiety and somatoform disorders, were largely consistent with past research. For example, other studies have reported elevated anxiety and hypochondriasis symptoms in PMD patients.[3, 9, 12]
Furthermore Johnson et al.
found that PMD patients had higher rates of simple phobia, OCD, and somatization disorder. Consistent with the findings of Serretti et al.
PMD patients in this study also had higher rates of cluster A disorders, particularly paranoid personality disorder. In contrast, we failed to find any consistent evidence for differences between PMD and NMD patients in family history of psychiatric illness. Although some studies have found higher family prevalence of affective disorders (e.g., Leckman et al.
) the majority have not.
It should be noted that self-reports of family history in this study were not independently verified.
The finding of higher rates of PTSD in patients with PMD extended the findings from a previous report from this data set that examined a smaller subsample (n
= 19) of these patients.
It also is consistent with other research showing similar trends of high PTSD comorbidity in PMD.
In the current study, diagnosticians were trained to carefully distinguish between psychotic symptoms and common PTSD symptoms, such as flashbacks and dissociative experiences. Only when the perceptual disturbances were outside the realm of the trauma-related material was PMD diagnosed. Still, high rates of PTSD comorbidity remained in the PMD sample, suggesting that trauma exposure may represent a diathesis for psychosis, which is suggested by emerging evidence.
Especially in patients with mood disorders, clinicians often focus on the differentiation of “real” or “true” psychotic symptoms from the so-called “pseudo” symptoms (e.g., transient psychotic experiences sometimes reported in individuals with borderline personality disorder). However, research suggests that patients classified as having “false” psychotic symptoms are still at risk for the later development of threshold psychotic symptoms and the need for treatment.
Furthermore, research examining internally versus externally perceived hallucinations fails to support the validity of this often used clinical heuristic.
Based on research showing higher than expected rates of “psychotic-like” experiences and schizotypal personality traits in the general population, there is a growing recognition that psychotic symptoms may best be viewed as falling along a continuum of severity.
The study of patients with PMD may be particularly helpful for investigating the quasi-dimensional qualities of psychotic symptoms.
One interesting finding was that the majority of PMD patients in this sample exhibited hallucinations (80%) in contrast to delusions (32%). Current DSM-IV criteria require only that delusions or
hallucinations to be present for a diagnosis of PMD. However, early studies on PMD tended to focus on samples of patients with delusional depression
Furthermore, many past studies of PMD samples have included patients with higher rates of delusions relative to hallucinations.[2, 3, 14]
Again, these differences in psychotic feature frequencies may be attributable to our examination of an entirely outpatient sample; whereas most previous studies were conducted in acutely ill inpatient samples. As discussed above, the differences observed between PMD and NMD outpatients in this study were largely consistent with those reported in past research in inpatient samples. However, some of the discrepancies in our findings may be partly due to the types and frequencies of psychotic symptoms in the current sample. Some have argued that there may exist important differences between PMD patients exhibiting primarily delusions versus hallucinations.
It will be important for future research to compare and contrast the clinical characteristics of PMD patients based on their psychotic symptom presentation.
There are several important clinical implications that can be derived from the current findings. First, results indicated that DSM-IV diagnoses of PMD were present in a relatively small group of treatment-seeking outpatients, but that these individuals were experiencing very high levels of severity and impairment. PMD outpatients can be viewed as similar to other severely mentally ill populations, such as schizophrenia and bipolar disorder, with lower absolute prevalence rates but disproportionately high levels of illness chronicity and associated disability. The high rates of comorbidity found in PMD patients indicate that the use of comprehensive semi-structured interviews administered by trained diagnosticians may be necessary to properly identify and differentially diagnose patients with PMD. As such assessments are not commonly employed in routine practice settings, the identification of outpatients with this disorder may continue to prove difficult.
Second, the high levels of severity and impairment observed in PMD outpatients are likely to be associated with treatment resistance.
PMD patients in our sample had approximately four times greater odds of chronic depression and suicide attempts and over two times greater odds of psychiatric hospitalization and chronic work impairment. Given the decreased efficacy of standard pharmacological treatments with PMD patients,[7, 55]
possible adjunctive interventions require careful consideration. Systematic reviews have concluded that the current evidence for the efficacy of adjunctive antipsychotic medication remains unclear.
Electroconvulsive therapy has been shown to be efficacious for PMD patients,
but the problems posed by treatment acceptability, potential side effects, and limited availability in many areas keep it from being a first-line treatment choice. Other approaches, such as adjunctive psychotherapy for depression appear particularly promising, although research on the efficacy of psychosocial interventions in PMD patients specifically remains in the preliminary stages.[24, 58]
Given the high levels of anxiety disorder comorbidity and recent advances made in the adaptation of behavioral interventions for psychotic patients,
psychotherapy that can be provided in addition to pharmacotherapy may be an attractive and feasible option for many outpatients.
Finally, it is important to note that our findings indicate that PMD patients are more likely to be members of disadvantaged groups who may be experiencing unique challenges that may also be related to their socioeconomic status. This finding combined with the lower rates of PMD found in the current outpatient sample suggests that specific community outreach efforts may be needed for individuals suffering from this illness. It is clear that aggressive treatment of PMD remains essential. Vythilingam et al.
found that PMD patients followed prospectively for up to 15 years after an index hospitalization had over twice the mortality rate of NMD patients (41 versus 20%) even after controlling for age and medical illness. Thus, clear challenges are faced by clinicians working with outpatients with PMD, and improvements in screening and treatment are critically needed for this high-risk clinical population.