Questionnaire-based diagnosis of hidradenitis suppurativa: Specificity, sensitivity and positive predictive value of specific diagnostic questions

Background Estimates of the prevalence of hidradenitis suppurativa (HS) range from 0·33% to 4%. Further epidemiological data are therefore needed. Because of the hidden nature of the disease, physical screening may be cumbersome and questionnaire-based screening may be more appropriate. Objectives To establish the sensitivity (SE), specificity (SP) and positive predictive value (PPV) of simple diagnostic questions used in HS. Methods Potential diagnostic questions regarding HS were identified and sent to 85 patients with HS and to an age- and sex-matched control group randomly selected among outpatients not being treated for HS. All respondents were recruited in the Department of Dermatology in Roskilde Hospital. Results In total, 74 of 85 patients with HS (87%) returned the questionnaire (61 women and 13 men). Of these, 72 reported repeated outbreaks of painful nodules or boils in locations typical for HS compared with 13 patients in the control group. The SE ranged from 0·92 to 0·97, the SP from 0·82 to 0·86 and the PPV from 0·85 to 0·89. Boils appeared significantly more often in patients with HS, who also reported significantly greater suffering from their lesions. Conclusions The high diagnostic power suggests that all the questions are potentially useful. The clear symptomatology of HS may be a key factor. It is suggested that further improvement may be achieved by adding definitions of pimples, nodules or boils to future questionnaires. Similarly, adding the possibility to indicate uncommon locations, duration and quality-of-life impairment may benefit the diagnostic power.