Systemic juvenile idiopathic arthritis and macrophage activation syndrome: Viva

This oral is built to probe the reasoning that holds the recognition and the early treatment of the macrophage activation syndrome at the centre, and to expose the candidate who has memorised the headline without the corners. The questions escalate from the classification and the pathogenesis to the biologic treatment, the recognition of the MAS, and the management of the paradoxical and the refractory cases. ^[9]

Opening question: the classification and the pathogenesis

The examiner opens with the presentation and asks how you classify her disease and what the modern understanding of the pathogenesis is. ^[2]

A strong answer names the ILAR classification of the systemic subtype, with the quotidian fever for at least two weeks plus the arthritis and the extra-articular features, and then the reframing of sJIA as Still disease, the autoinflammatory disease driven by the innate-immune interleukin-one and interleukin-six axis. The interleukin-one-beta drives the quotidian fever and the rash, the interleukin-six drives the acute-phase response, and the interleukin-eighteen primes the immune system for the macrophage activation syndrome. ^[9]

Model answer. This girl has systemic juvenile idiopathic arthritis by the ILAR criteria, with the quotidian fever, the evanescent rash and the arthritis. The modern understanding is that sJIA is an autoinflammatory disease of the innate immune system, driven by the interleukin-one-beta and the interleukin-six, not the adaptive-autoimmune pathways of the other subtypes. This is why the interleukin-one and the interleukin-six blockade is the first-line treatment. ^[2][9]

Pitfall probe. Why is the methotrexate less effective for the systemic features of sJIA than for the polyarticular subtypes? Because the methotrexate targets the adaptive immunity, while the systemic features are driven by the innate-immune cytokines. The methotrexate may help the arthritis but not the fever and the rash. ^[9]