Systemic juvenile idiopathic arthritis and macrophage activation syndrome: SAQ

This girl has the classic presentation of systemic JIA and the subsequent development of the macrophage activation syndrome under the tocilizumab, which is the scenario that tests the candidate on the ILAR criteria, the 2016 MAS classification, the interleukin-one and interleukin-six pathway, and the management of the paradoxical MAS. ^[1]

Question 1 (10 marks)

Outline the ILAR classification criteria for the systemic subtype of juvenile idiopathic arthritis, and then describe the 2016 EULAR ACR PRINTO classification criteria for macrophage activation syndrome complicating systemic JIA, applying them to this girl's presentation. ^[1]

A full-mark answer reproduces the ILAR criteria, the 2016 MAS criteria and their application. ^[2]

The ILAR criteria for systemic JIA (4 marks). The child must have arthritis in one or more joints, with or preceded by a quotidian fever for at least two weeks documented for at least three days of each week, plus at least one of four extra-articular features: an evanescent non-fixed erythematous rash, a generalised lymphadenopathy, a hepatomegaly or splenomegaly, and a serositis. The onset must be before sixteen years and the duration at least six weeks. The exclusions include a personal or a first-degree family history of psoriasis or HLA-B27, and a first-degree family history of systemic JIA. ^[2]

The 2016 MAS criteria (4 marks). A febrile patient with known or suspected sJIA is classified as having MAS if the ferritin is over six hundred and eighty-four nanograms per millilitre and any two or more of the following are present: a platelet count under one hundred and eighty-one times ten to the nine per litre, an AST over forty-eight units per litre, triglycerides over one hundred and fifty-six milligrams per decilitre, and a fibrinogen under three hundred and sixty milligrams per decilitre. These criteria have a sensitivity of around seventy-three percent and a specificity of around ninety-nine percent. ^[1]

Application to this girl (2 marks). This girl meets the ILAR criteria with her quotidian fever, her evanescent rash and her arthritis. She meets the 2016 MAS criteria with her ferritin at four thousand two hundred and her platelets at one hundred and sixty under the one hundred and eighty-one threshold, which gives the ferritin criterion plus at least one additional criterion. The full picture with the AST, the triglycerides and the fibrinogen would be needed to confirm the two additional criteria, but the clinical picture is strongly suggestive of the MAS. ^[1]