Bipolar disorder in patients with psoriasis, and the impact of lithium therapy on psoriasis

There is a significant amount of research examining the link between psoriasis and common mental health disorders; however, studies on less common psychiatric disorders, such as bipolar disorder (BD), remain limited. We conducted a systematic review of studies in the PubMed and Cochrane databases that explored the relationship between BD and psoriasis. Additionally, we evaluated the impact of lithium on psoriasis in patients with BD and included a quality assessment of all the studies. This review covers five studies that addressed the connection between psoriasis and psychiatric disorders, three studies on medical conditions in patients with BD, and four studies examining the effects of lithium intake on psoriasis in BD patients. We found substantial evidence supporting a link between psoriasis and BD, suggesting that psoriasis is an independent risk factor for BD. Patients with psoriasis are also more likely to use psychotropic medications. A limited number of studies indicate that lithium therapy may trigger or worsen psoriasis. We also explore the mechanisms of lithium-induced or -aggravated psoriasis, highlighting the intricate interplay between lithium treatment, inositol depletion, and psoriasis in patients with BD. In a placebo-controlled, randomized study, inositol supplementation could mitigate psoriasis in patients taking lithium. Additional research is needed to evaluate the efficacy of inositol supplementation for patients with psoriasis who need to continue lithium treatment for their BD. Psoriasis is a chronic inflammatory skin disease affecting 2-3% of the global population.¹ It is characterized by an abnormal immune response involving dendritic cells, T helper (Th)1/Th17 lymphocytes, and keratinocytes, each engaging in a pathologic interplay that leads to systemic effects mediated by the cytokine milieu beyond skin changes.^2,3 Psoriasis has a significant impact on the quality of life of affected individuals.⁴ Patients with psoriasis, especially those with severe forms, experience numerous comorbidities, including psychiatric disorders.^5-15 People who suffer from psoriasis face an increased risk of developing various mental illnesses, including depression and anxiety,^13,16 potentially linked to the increased inflammatory cytokine burden that affects neuropsychiatric pathways.^13,17 The visible effects of psoriasis may also lead to significant stress, reduced self-esteem, and stigma, further contributing to adverse psychiatric outcomes.¹⁸ There is significant amount of research concerning the link between psoriasis and common mental disorders, such as major depressive disorder (MDD).^3,13,14 Studies on less common psychiatric disorders, like bipolar disorder (BD),^12,15,16 remain limited. BD affects approximately 1-3% of the global population and is characterized by alternating episodes of depression and mania (or hypomania). It leads to considerable changes in mood and energy levels, resulting in severe impairments in personal, social, and occupational functioning. Lithium is a well-established treatment for BD and is effective for managing acute mania and maintaining mood stability. Lithium possesses mood-stabilizing, antimanic, antidepressant, and anti-suicidal properties;¹⁹ however, its use can often complicate matters, because it may trigger or worsen psoriasis, which in turn significantly contributes to non-compliance with lithium therapy.²⁰ The mechanisms by which lithium affects psoriasis remain poorly understood, with there being limited literature exploring psoriasis in patients with BD who are receiving lithium therapy.