Demographic and clinical correlates of extent of psoriasis during stable disease and during flares in chronic plaque psoriasis

Summary Background  Following a previous population‐based study, we define a common psoriatic phenotype (A) with a limited area of involvement of stable disease but extensive flares and a less common phenotype (B) with consistently widespread disease. Objectives  To define these phenotypes quantitatively and to investigate any biological significance through correlations with clinical disease characteristics. Psoriatic plaque thickness was also included in the analyses. Methods  Two hundred and ninety‐four patients who had had chronic plaque psoriasis for at least 5 years were recruited. Area of involvement during stable disease ( A basal ) and during the most severe flare ( A max ) were derived from current area of involvement and patient history. Mean plaque thickness ( T ) was calculated from a current Psoriasis Area and Severity Index score. Results  Multivariate regression of each variable on A basal , A max and T showed many highly significant relationships. Usually A basal and A max were retained in the final models but with some variables only A basal was retained, suggesting an intrinsic effect unrelated to A max . Phenotype A was associated with female gender, age at onset < 40 years, exacerbation by sore throat and stress, decreased concern about psoriasis and good response to ultraviolet B and methotrexate. A basal was individually associated with nail and joint involvement and need for second‐line therapy. T was related to male gender, nail involvement and decreased exacerbation by stress on univariate analysis but only to nail disease on multivariate analysis. Conclusions  The phenotypes have been shown to have biological significance. A basal and A max may be useful therapeutic indices of long‐term severity in clinical trials and in the investigation of genetic/environmental influences on psoriasis severity.