COVID-19 and cytokine storm syndrome: are there lessons from macrophage activation syndrome?

Although interest in "cytokine storms" has surged over the past decade, it was massively amplified in 2020 when it was suggested that a subset of patients with COVID-19 developed a form of cytokine storm. The concept of cytokine storm syndromes (CSS) encompasses diverse conditions or circumstances that coalesce around potentially lethal hyperinflammation with hemodynamic compromise and multiple organ dysfunction syndrome. Macrophage activation syndrome (MAS) is a prototypic form of CSS that develops in the context of rheumatic diseases, particularly systemic juvenile idiopathic arthritis. The treatment of MAS relies heavily upon corticosteroids and cytokine inhibitors, which have proven to be lifesaving therapies in MAS, as well as in other forms of CSS. Within months of the recognition of SARS-CoV2 as a human pathogen, descriptions of COVID-19 patients with hyperinflammation emerged. Physicians immediately grappled with identifying optimal therapeutic strategies for these patients, and despite clinical distinctions such as marked coagulopathy with endothelial injury associated with COVID-19, borrowed from the experiences with MAS and other CSS. Initial reports of patients treated with anti-cytokine agents in COVID-19 were promising, but recent large, better-controlled studies of these agents have had mixed results suggesting a more complex pathophysiology. Here, we discuss how the comparison of clinical features, immunologic parameters and therapeutic response data between MAS and hyperinflammation in COVID-19 can provide new insight into the pathophysiology of CSS.