Body mass index, waist circumference and HOMA-IR correlate with the Psoriasis Area and Severity Index in patients with psoriasis receiving phototherapy

Abstract

Funding sources: This work was funded by an unrestricted research grant from Merck Serono Ltd and Abbott Laboratories Ltd and the Postgraduate Medical and Dental Board of Ireland. Conflicts of interest: none declared. Dear Editor, An increased incidence of obesity in patients with psoriasis has been documented in cross‐sectional studies of large healthcare databases and case–control studies.1 2 3 4 5 6 7 Obesity, and in particular centripetal obesity, confers a risk of developing insulin resistance and type 2 diabetes, which in turn increases the risk of cardiovascular disease. Since 1978 it has been known that patients with psoriasis have higher rates of type 2 diabetes and cardiovascular disease and it is likely that this is driven by obesity and concomitant insulin resistance. We undertook a study to establish the effect of body mass index (BMI), abdominal obesity and insulin resistance on psoriasis severity and Framingham risk. Following ethical approval, consecutive patients with psoriasis, aged ≥ 18 years, were recruited prior to commencing phototherapy or photochemotherapy (TL‐01 or psoralen plus ultraviolet A) between October 2008 and July 2011. Patients had a full physical examination and the Psoriasis Area and Severity Index (PASI) score was recorded. Height, weight and waist circumference were measured for each patient. The BMI was calculated using the formula: weight in kg/(height in m)2. Obesity was defined as a BMI > 30, overweight as BMI 25–30 and lean as a BMI < 25 according to the World Health Organization definition of obesity. Systolic blood pressure was measured using a sphygmomanometer on the left brachial artery. Fasting blood samples were taken for the measurement of insulin, glucose and serum cholesterol. Insulin resistance was measured using the homeostasis model with the formula: insulin × glucose/22·5 (HOMA‐IR, homeostatic model assessment–insulin resistance). Framingham risk was calculated using MedCalc® (MedCalc Software, Ostend, Belgium). Results were analysed using GraphPad Prism (GraphPad Software Inc., La Jolla, CA, U.S.A.), using Student's t‐test, anova and Pearson's rank correlation.