The Prevalence of Psychiatric Comorbidity in Patients with Prurigo Nodularis.

BACKGROUND: Prurigo nodularis (PN) is a chronic, recalcitrant itchy dermatosis. It is supposed to be associated with psychological factors, but research in this area is scarce.
OBJECTIVES: To study the prevalence and determinants of psychiatric morbidity, and the phenomenology of itch in PN.
MATERIALS AND METHODS: This study was carried out in the outpatient service of the Department of Dermatology. Purposive sampling was used to recruit 50 patients each with PN, chronic urticaria (CU), and vitiligo (V). A one-time cross-sectional assessment was carried out on the participants. Psychiatric morbidity was assessed using Mini-International Neuropsychiatric Interview and Patient Health Questionnaire-9.
RESULTS: The three groups were comparable on socio-demographic parameters. The prevalence of any psychiatric disorder (current or lifetime) was 48%, 42%, and 58% in the PN, CU, and V groups, respectively (P = 0.27). LIMITATIONS: The limitations of this study include the small sample size and the purposive, non-blind nature of assessments.
CONCLUSION: Our study suggests that there is significant psychiatric morbidity in PN which is comparable to that seen in CU and V.

Introduction

Prurigo nodularis (PN) is a chronic, difficult-to-treat, itchy dermatosis of unknown etiology.[1] PN is supposed to be influenced by and associated with psychological factors, but research in this area is scarce. Some studies have focused on psychological symptoms and traits and found that anxiety and depressive symptoms and traits such as alexithymia are common in patients with PN.[23] A clinic-based study showed that dermatological outpatients diagnosed with common mental disorders included patients with PN.[4] Another population registry-based audit showed that patients with PN are commonly diagnosed with anxiety and depressive disorders and are often prescribed psychotropics.[5]

The above review of literature suggests the need for a comprehensive, controlled study using standardized techniques into the prevalence of psychiatric morbidity (PM) in PN. The aim of this study was to assess the PM in a cohort of patients with PN and compare it with two control groups.

Materials and Methods

This study was carried out in the outpatient service of the Department of Dermatology, Venereology and Leprology of a tertiary care hospital. The work was approved by the institute ethics committee. Purposive sampling was used to recruit 50 patients each with PN, chronic urticaria (CU), and vitiligo (V). Written informed consent was obtained. CU and V were included as controls because they are relatively better-studied conditions with respect to PM, and second as these represent a chronic itchy and a non-itchy dermatoses, respectively. Inclusion criteria for the study were adults (>18 years) with a diagnosis of PN, V, or CU who can read Hindi or English. The diagnosis of PN, CU, and V was confirmed by dermatologists using standard clinical and laboratory diagnostic criteria. Patients with organic brain syndrome, mental retardation, and current substance intoxication were excluded. The treatment of patients was carried on as usual.

A one-time cross-sectional assessment was carried out on the participants. Socio-demographic data and clinical profile sheet developed for this study were used. PM was assessed using Mini-International Neuropsychiatric Interview (MINI), and the severity of depressive symptoms was assessed using Patient Health Questionnaire-9 (PHQ-9).[67] MINI is a brief, validated, clinician-rated instrument that generates World Health Organization 10th revision of the International Statistical Classification of Diseases and Related Health Problems (ICD-10) and American Psychological Association Diagnostic and Statistical Manual of Mental Disorders, 4th Edition (DSM-IV) psychiatric diagnoses. MINI was administered by a psychiatrist. PHQ-9 is a self-administered brief questionnaire that generates diagnoses of depression and also severity of depressive symptoms. The suite of PHQs is available at www.phqscreeners.com. In this study, a Hindi version of PHQ-9 available online was used. Quality of life (QOL) assessment was done with Dermatological Life Quality Index (DLQI).[8] Data were analyzed using Statistical Package for Social Sciences software, version 18.0 (SPSS).[9]

Results

A total of 150 patients of three dermatoses were recruited and studied. Table 1 presents the socio-demographic and clinical profile of the participants in the study. The three groups were comparable on socio-demographic parameters. The prevalence of any psychiatric disorder (current or lifetime) was 49.3% (n = 74) in the whole study population. It was 48%, 42%, and 58% in the PN, CU, and V groups, respectively (P = 0.27). There was no statistically significant difference between the prevalence of psychiatric disorders among any of the three groups (PN and V: Chi-square P = 0.31; PN and CU: Chi-square P = 0.54; CU and V: Chi-square P = 0.11). The distribution of type of psychiatric disorders also shows that comorbid disorders (more than one psychiatric diagnosis) was more common than individual psychiatric disorders. Males had a higher prevalence of comorbid disorders than females. Table 2 presents the details of the MINI diagnoses in the three groups. Current episodes rather than past episodes of depressive and anxiety disorders were most common across the three groups.

Table 1

Socio-demographic and clinical profile of the study population

Table 2

Details of MINI diagnoses (positive screens only)

The impairment in QOL was statistically comparable across the three groups [mean DLQI scores: PN = 17.28 (10.32), V = 18.62 (9.58), CU = 14.80 (10.35); analysis of variance (ANOVA) P = 0.16]. The severity of depressive symptoms was also comparable across the three groups (mean PHQ scores: PN = 12.20 (7.59), V = 11.66 (7.00), CU = 9.86 (7.49); ANOVA P = 0.25). These scores indicate moderate depressive severity across the three groups.

Discussion

The interface between dermatology and psychiatry is inevitable, complex, and of clinical importance. Chronic nature of the dermatoses, stress related to dysfunction, disfigurement, impaired QOL, and stigma associated with skin disorders are likely to be responsible for this association.

We conducted a study using purposive sampling in patients with PN and compared the results with patients suffering from CU and V. The choice of comparison groups was guided by the following factors. First, PN is a poorly studied disorder and we wanted to compare the different psychiatric variables in PN against those observed in dermatoses with known and replicated psychological morbidity and impairment in QOL. Second, we wanted to compare PN with an itchy and a non-itchy chronic dermatosis. Although the nature of itch and determinants of psychological comorbidity may vary in these three conditions, we wanted to assess whether the psychological comorbidity and impairment in QOL were comparable across these common dermatoses irrespective of putative reasons.

We found that there was comparable PM across the three groups even though there were gender differences. The prevalence was similar to another study using the same instrument done in patients with psoriasis from this center.[10] Earlier studies done from this center on patients with V using clinical interviews and other instruments found somewhat lower prevalence of PM.[1112] A study on PM in CU using standardized clinical diagnostic instrument found a prevalence of 60%.[13] The differences of prevalence of common mental disorders in people with physical illnesses are mostly due to methodological differences.[14] The results of previous studies and our study using similar instruments show that PN, CU, and V have comparable and significant PM. This is underscored by the PHQ-9 score where the mean score was suggestive of mild to moderate depressive symptomatology. The individual diagnoses were along expected lines in that depressive and anxiety disorders were the most common. This is in keeping with the findings across most psychosomatic research in clinic- and community-based populations with physical illness.[15] We found that more males than females were found to be suffering from PM. This is contrary to most studies that report a preponderance of females due to biological and psychosocial factors.[16] One possible reason for our findings could be that overall males had greater impairment in QOL when compared with females especially in patients with PN [mean DLQI males = 23.00, standard deviation (SD) = 5.69; females = 13.13, SD = 10.99; P ≪ 0.05]. This was pronounced in the domains of feeling embarrassed due to skin condition (item 2) and finding treatment problematic (item 10). Impairment in QOL has been shown to be an important statistical factor in the genesis of PM in patients with dermatological conditions such as psoriasis.[16] There is also well-documented and replicated association between impairment in QOL and psychological comorbidity in other chronic illnesses such as diabetes.[17] This association is likely to be bidirectional, and proper screening for and management of psychiatric comorbidity and treatment of the skin condition aimed at improvement of QOL may positively influence each other.

Our results show that patients with PN have comparable and significant PM, impairment in QOL, and depressive symptomatology when compared with the better-studied conditions of CU and V.

The limitations of this study include the small sample size and the non-blind nature of assessments. However, many of the instruments were self-rated. We also did not control for any possible impact that treatment modalities may have had on the variables that were studied.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.