Risk of Cataracts among Idiopathic Thrombocytopenic Purpura (ITP) Patients in the UK General Practice Research Database (GPRD).

ITP is a disease caused by inadequate platelet production as well as increased platelet destruction. Oral systemic steroids are recommended as first-line treatment. Prolonged use of oral steroids in other disease populations has been associated with an approximately two-fold increase in the risk of developing a cataract. This study aimed to quantify the underlying risk of cataracts among ITP patients compared with non-ITP patients. Using the GPRD, a retrospective matched cohort study was conducted in which each ITP patient newly diagnosed between 1992 and 2005 and age 18 years or older was matched to 5 non-ITP patients on gender, age, practice and duration of follow-up. ITP patients and cataract events were identified using specific Read/Oxmis disease codes and validated by a clinical epidemiologist. The exposure of interest was oral steroid use and the primary outcome was cataracts (recorded as cataracts or cataract surgery). Patients with a history of cataracts were not excluded from the study. Potential covariates of interest were diabetes, schizophrenia, glaucoma, splenectomy and hypertension. The risk of cataracts was quantified using incidence rates and 95% confidence intervals (CI) and, the difference between groups was estimated using a rate ratio and 95% CI. All analyses were further stratified by age and gender. Adjusted rate ratios were estimated using the Cox proportional hazard model. Seven hundred sixty ITP patients were identified, 745 (98%) of whom had 5 matched controls. The entire sample had a mean age of 56.4 years and 60.1% were female. Among ITP patients, users of oral steroids had a cataract incidence rate of 14.0 per 1000 person-years (PY) (95% CI: 8.7 – 21.4) and non steroid users 6.1 per 1000 PY (95% CI: 2.7 – 11.4). In the non-ITP population, these figures were 16.9 per 1000 PY (95% CI: 11.9 – 23.3) and 9.2 per 1000 PY (95% CI: 7.6 – 11.0), respectively. The incidence of cataracts was observed to increase with age. Adjusting for steroid use and other factors, the risk of cataracts was similar in the ITP and non-ITP populations (adjusted rate ratio 0.8, 95% CI: 0.5 – 1.2) whereas, oral steroid use was associated with an increased risk of cataracts in both ITP and non ITP populations (adjusted rate ratio 1.6, 95% CI: 1.2 – 2.2). There was no evidence of increased risk with either inhaled steroids, or intranasal steroids. As expected, our study shows that the use of oral steroids is associated with an increased risk of cataracts in both ITP and non-ITP populations. However, we found no evidence of a difference in the risk of cataracts between an ITP and a matched non-ITP population.