24th February 2025

Overview of AOSD

AOSD can be thought of as being on the same continuum as systemic-JIA. It is a rare, muti-system inflammatory disorder, affecting males and females equally, with a bimodal incidence in the late teens/early 20s and the late 40s/early 50s. The cause is unknown, though there is thought to be a genetic preponderance in patients with certain HLA subtypes. It can be triggered by pregnancy, and the index presentation may occur in the postpartum period. Various infections have also been identified as triggers, including viral (CMV, EBV, Coxsackie) and bacterial (Mycoplasma pneumoniae and Chlamydia pneumonia) infections.

The pathophysiology of the response seen in AOSD is similar to that in RA, being mediated by lymphocytes and a ‘cytokine storm’ thought to involve IFN-ɣ, TNF-ɑ and IL-6, among other markers. The principles of treatment and, indeed, the agents used are similar to those used in RA and systemic-JIA, including in the case of secondary HLH, usually guided by a Rheumatologist. There are three patterns of AOSD, with an approximately equal split: monophasic (a single episode with remission within one year); polycyclic systemic (recurrent flares with periods of remission, typically separated by years); and chronic articular (mainly affecting the joints causing a severe, destructive and disabling arthritis).