Psoriasis and Schizophrenia: An Interesting Association

Dear Editor, Among all psycho-dermatologic associations, one of the most discussed topic is the striking relation between psoriasis and schizophrenia. There are multiple controlled trials as well as meta-analyses on this subject and interesting theories have been developed. We are trying to compile and concise the available information and to present it in a structured way for better understanding, through this letter.

Relation in etiopathogenesis Multiple theories have been put forward. Most accepted hypothesis is the association with common cells (Th-17) and mediators (TNF-alpha, IL-2) in both the conditions (1, 2). Role of Th-17 cells in initiation and progression of schizophrenia have been suggested by multiple studies. Mild encephalitis hypothesis also support the role of inflammation and pro-inflammatory cells in the pathogenesis of schizophrenia (3). In genomic analysis, a locus for schizophrenia has been recently discovered on 6p region, near to the loci for psoriasis (PSOR₁) (4). These loci were overly expressed in major cells in immunity, eg. B cells, which has central role in pathogenesis of psoriasis too. These findings support genetic association of both the disorders. Some researchers have opined association as a result of confounders like substance abuse, which has a higher prevalence among schizophrenic patients but is also an important risk factor for psoriasis.

Evidences for the association In a comprehensive systematic review study of all cohort and case control studies done by Ungprasert et al, they have found a significantly higher prevalence (1.83 fold) of psoriasis among schizophrenic patients (5). But most of the articles they analyzed were retrospective studies using electronic medical records, which are known to have low sensitivity and specificity. Kumar et al observed paranoid schizophrenia in 3.3% of psoriasis patients in a cross sectional study conducted among Indian patients (6). There are multiple case reports and case series showing their co-occurrence and related course of disease.

Effect of treatment of one disease on the other Typical antipsychotics have beneficial effect on psoriasis as reported by Miyaoka et al. with haloperidol and levomepromazine in two separate patients as well as by Shimamoto et al. with chlorpromazine (7, 8). But on contrary, atypical antipsychotics seems to have harmful effect on psoriasis. In multiple case reports olanzepine dramatically worsened pre-existing psoriasis (9, 10). On the other hand, some drugs used for psoriasis were also reported to affect the course of psychosis. Di Nuzzo et al. reported worsening of psychotic symptoms in a patient with plaque psoriasis and paranoid schizophrenia, few weeks after the initiation of cyclosporine therapy for psoriasis (2). Similarly Kaufman et al reported manic episode in psoriasis patient following administration of TNF-alpha inhibitor, etanercept (11). Both the cases reflect the role of similar chemical mediators in both conditions.

Conclusion

Overlapping nature of chronic dermatological disorders and psychiatric diseases demands careful assessment from the experts of both sides. Dermatological evaluation of skin rashes in schizophrenic patients is mandatory for early detection and treatment of psoriasis. Since psoriasis itself can affect quality of life significantly, liaison clinic approach will be promising. Knowledge about the relationship in pathogenesis of both the diseases will help the treating doctor to choose drugs wisely so that other disease will not be worsened.