To ASLO or Not to ASLO: Utility of the ASLO Test in Dermatology

BACKGROUND: Group A Streptococcus (GAS) causes a wide spectrum of acute infections and immune-related diseases, most of which include a dermatological presentation. However, dermatological findings have a wide range of other possible etiologies. The diagnosis of GAS-related disease requires an indication of preceding GAS infection by direct culture or by measuring antistreptolysin O (ASLO) titer. OBJECTIVES: To explore the correlation between ASLO positivity and dermatological diseases. METHODS: We analyzed clinical data from all cases of patients over 18 years of age who underwent ASLO testing between the years 2016 and 2020 in the Department of Dermatology at Rambam Health Care Campus. RESULTS: Of 152 adult patients with ASLO tests, 100 had diagnoses that were potentially related to streptococcal infection. Vasculitis and psoriasis were the most suspected diagnoses. Positive ASLO test was found in 44 (29%) patients. The diagnoses showing the highest ratio of positive ASLO were psoriasis (60%), erythema nodosum (46%), skin infections (43%), Sweet syndrome (33%), and vasculitis (15%). Psoriasis types included plaque psoriasis (8 patients), guttate psoriasis (3 patients), and palmoplantar pustulosis and erythroderma (2 patients each). CONCLUSIONS: Although the applicability of ASLO for the spectrum of dermatological diseases remains unclear, our results enhance the practical relevance of the test. We showed a higher prevalence of positive ASLO tests in psoriasis and erythema nodosum cases and a lower prevalence in vasculitis. Notably, ASLO was positive in all psoriasis subtypes, suggesting high utility of the test for psoriasis.