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The use of online peer support communities in dermatology

tify how often patients have palmoplantar pustulosis and also how often patients with palmoplantar pustulosis have coexistent plaque psoriasis. They analyse insurance claims and registry data from three countries looking at how often patients diagnosed as having palmoplantar pustulosis [defined by a claim with International Classification of Diseases (ICD-10) code L40 3] also had a diagnosis of psoriasis (defined as having another claim with an ICD-10 code of L40 0 or ICD-9 code of 696 1). As a means to fully understand how common a distinct entity of palmoplantar pustulosis is and how often it is associated with a truly separate condition of psoriasis, this approach is, of course, doomed to fail from the get-go. On the other hand, this approach may tell us a lot about the variability in how these conditions are characterized and the difficulty we currently have in definitive diagnosis of these patients. Andersen et al. studied data from Germany, Denmark and the U.S.A. We would not expect much difference between the true prevalence of palmoplantar pustulosis or psoriasis between these populations (particularly not, from our U.S. perspective, between Denmark and Germany; we cannot tell them apart). However, the U.S., Danish and German prevalences of palmoplantar pustulosis varied over ten-fold, from 0 005% in the Danish population to 0 08% in the German population. Moreover, the prevalence of psoriasis in patients with palmoplantar pustulosis varied dramatically as well, from 14 2% in the Danish population to 61 3% in the U.S. population; in contrast, the prevalence of psoriatic arthritis in the patients with palmoplantar pustulosis showed little variation (11 9–14 6%). Perhaps palmoplantar pustulosis is a distinct entity that is 16 times more common in Germany than in Denmark. We think it is more likely that this study is telling us that the current categorization of patients with palmoplantar pustular disease is based on something other than different pathophysiological states. Right now, we often want to treat such patients with biologics, and in the U. S. A., biologics are approved only for plaque-type psoriasis; knowing that, it did not surprise us that U.S. patients with palmoplantar pustulosis are also said to have plaque psoriasis most of the time. Likely, many more U.S. patients with palmoplantar pustular conditions are simply diagnosed and treated as having psoriasis and never get a palmoplantar pustulosis designation. Should a drug be approved specifically for the treatment of palmoplantar pustulosis, we are confident that the number of people who are diagnosed as having palmoplantar pustulosis will increase dramatically. There is value in determining how many people truly have a distinct entity of palmoplantar pustulosis and what the relationship is between palmoplantar pustulosis and psoriasis, especially since such information is likely to have important treatment implications. For now, though, we will name these conditions based on the current practical implications until we get better diagnostic approaches, perhaps genetic ones, that define these entities on a more scientific basis. Conflicts of interest