BACKGROUND: Observations in controlled trials and case reports have linked lithium exposure to induction or exacerbation of psoriasis. A causal relationship between lithium exposure and incident psoriasis has been questioned, and observational studies are lacking. METHODS: We conducted a case-control analysis using the United Kingdom-based General Practice Research Database to study the association between the use of lithium or antipsychotics and the risk of developing an incident diagnosis of psoriasis. We identified cases with an incident diagnosis of psoriasis between 1994 and 2005, and controls were matched to the cases on age, sex, general practice, calendar time, and years of history in the database. We used conditional logistic regression to estimate the risk of developing a first-time diagnosis of psoriasis in relation to previous exposure to lithium and antipsychotic drugs, stratified by exposure timing and duration. We calculated odds ratios (ORs) with 95% confidence intervals (CIs) adjusted for smoking, body mass index, and additional potential confounders. RESULTS: We identified 36,702 incident cases of psoriasis and the same number of matched controls. Compared with nonuse, current use of 5 or more prescriptions for lithium and atypical antipsychotics yielded adjusted ORs of 1.68 (95% CI, 1.18-2.39; P < 0.01) and 0.76 (95% CI, 0.55-1.06; P = 0.11), respectively. The OR for olanzapine was 0.50 (95% CI, 0.28-0.89, P = 0.02). CONCLUSIONS: Long-term use of lithium was associated with a small increase in risk of incident psoriasis. There was a suggestion of a possible reduced psoriasis risk associated with the use of atypical antipsychotics, mainly olanzapine, a finding that needs further evaluation.
BACKGROUND: Observations in controlled trials and case reports have linked lithium exposure to induction or exacerbation of psoriasis. A causal relationship between lithium exposure and incident psoriasis has been questioned, and observational studies are lacking. METHODS: We conducted a case-control analysis using the United Kingdom-based General Practice Research Database to study the association between the use of lithium or antipsychotics and the risk of developing an incident diagnosis of psoriasis. We identified cases with an incident diagnosis of psoriasis between 1994 and 2005, and controls were matched to the cases on age, sex, general practice, calendar time, and years of history in the database. We used conditional logistic regression to estimate the risk of developing a first-time diagnosis of psoriasis in relation to previous exposure to lithium and antipsychotic drugs, stratified by exposure timing and duration. We calculated odds ratios (ORs) with 95% confidence intervals (CIs) adjusted for smoking, body mass index, and additional potential confounders. RESULTS: We identified 36,702 incident cases of psoriasis and the same number of matched controls. Compared with nonuse, current use of 5 or more prescriptions for lithium and atypical antipsychotics yielded adjusted ORs of 1.68 (95% CI, 1.18-2.39; P < 0.01) and 0.76 (95% CI, 0.55-1.06; P = 0.11), respectively. The OR for olanzapine was 0.50 (95% CI, 0.28-0.89, P = 0.02). CONCLUSIONS: Long-term use of lithium was associated with a small increase in risk of incident psoriasis. There was a suggestion of a possible reduced psoriasis risk associated with the use of atypical antipsychotics, mainly olanzapine, a finding that needs further evaluation.