Abstract
Generalized pustular psoriasis (GPP) is a rare disease that has only recently benefited from a consistent definition and clinical coding standard. A lack of disease awareness combined with clinical similarities to other types of psoriasis have historically complicated the diagnosis of GPP. It is now clear that GPP requires a differential diagnosis from psoriasis vulgaris (plaque psoriasis), and better understanding of the genetic characteristics underlying GPP may improve the accuracy of diagnoses in the future. GPP can present at any age but is most common in the fifth decade of life. There appears to be a female preponderance in GPP, although there is notable variability in prevalence by geographical region and between ethnicities. GPP is potentially life-threatening, associated with several serious complications, and may require emergency treatment, particularly for complications arising from systemic inflammation. As with many rare diseases, there are inherent challenges to understanding the epidemiology of GPP. In addition to small patient numbers, estimating the prevalence of rare diseases is further complicated by studies that use non-standardized methodologies and that are conducted in different populations. These complications in data gathering have led to marked variability in GPP case estimates by geographical region and between ethnicities. There is ongoing research into disease characteristics, and insights into regional measures of prevalence are essential to increasing our understanding of GPP.