Comments on the Risk of Gout in Patients with Psoriasis [Letter]

Dear editor

We read with great interest the epidemiological study by Wei et al investigating the association between psoriasis and subsequent gout.¹ They indicated that patients with new onset psoriasis had a higher risk of subsequent incidence of gout. We thank the authors for adopting a nationwide database, covering near all Taiwan residents, thus partly avoiding detection bias and providing empirical evidence for this issue. However, we would like to share some ideas.

First, regarding psoriasis, as the researchers stated, a possible inherent limitation of retrospective studies derived electronic medical records is inaccuracy of coding diagnoses and thus misclassification.² The authors controlled for this bias by selecting those with ICD coding of the disease by specialists, such as dermatologists and rheumatologists, with corresponding medication. We commend them for their narrow definition of ICD-disease coding, which is a good model for any future authors planning to conduct claims-based studies. A recent study provided an algorithm that showed a positive predictive value of up to 95% in patients who had more than 1 examination by a dermatologist with psoriasis as the primary diagnostic code and a prescription for vitamin D derivatives as eligible participants.³ Here, we would like to highlight the importance of reporting case ascertainment, where authors can provide positive predictive rates based on ICD coding algorithms or perform sensitivity analyses using different scenarios to make the study results more trustworthy.⁴

Second, there seems to be no accounting for healthcare utilization after index date. Patients with or without psoriasis may have different behavioral and medical utility frequencies and are therefore susceptible to bias in the follow-up examination of their lingering symptoms.

Third, the severity of psoriasis is associated with subsequent metabolic disease,⁵ and it may be of interest to readers if the authors are able to dwell more on the impact of psoriasis severity on gout events.

Although a definitive effect of psoriasis on the risk of gout will require future studies to reach a final conclusion, we thank Wei et al for their excellent work and look forward to their response.