Systemic juvenile idiopathic arthritis and macrophage activation syndrome: Case

Framing the case

This four-year-old girl with the systemic JIA who develops the falling platelets and the rising ferritin under the tocilizumab with the normal CRP is the textbook presentation of the paradoxical macrophage activation syndrome. The framework that organises the case is the recognition that the interleukin-six blockade masks the usual warning signs of the MAS, so the diagnosis rests on the trend of the platelets and the ferritin rather than the fever and the CRP. [5]

The initial presentation and the diagnosis

The quotidian fever that returns to baseline, the evanescent salmon-pink rash, and the arthritis together fulfil the ILAR criteria for the systemic subtype of juvenile idiopathic arthritis. The negative autoantibodies, the leukocytosis and the thrombocytosis are the typical laboratory features. The modern understanding is that sJIA is an autoinflammatory disease driven by the innate-immune interleukin-one and interleukin-six axis, and the 2024 EULAR and PReS recommendations reframe it as Still disease. The first-line biologic is the interleukin-one blockade, and the tocilizumab is the interleukin-six blockade that was started in this case. [9]

The recognition of the paradoxical MAS

The falling platelet count from four hundred and eighty to one hundred and fifty and the rising ferritin from six hundred to three thousand eight hundred in a child whose disease appeared controlled are the signs of the macrophage activation syndrome. The normal CRP does not exclude the MAS because the tocilizumab suppresses the interleukin-six and the CRP, masking the usual inflammatory signal. The mechanism is that the tocilizumab blocks the interleukin-six but not the interferon-gamma, so the underlying interferon-gamma cytokine storm of the MAS continues beneath the masked exterior. [5][10]

The 2016 EULAR, ACR and PRINTO criteria are applied. The ferritin at three thousand eight hundred is over the six hundred and eighty-four threshold, and the platelets at one hundred and fifty are under the one hundred and eighty-one threshold. The AST, the triglycerides and the fibrinogen are checked to confirm the second additional criterion, but the clinical picture is already strongly suggestive of the MAS. [1]

The management of the MAS in this child

The tocilizumab is reduced or stopped, because the interleukin-six blockade is masking the syndrome without controlling it. The child is transferred to the paediatric intensive care unit for the monitoring and the supportive care. The first-line therapy bundle includes the intravenous methylprednisolone pulse at ten to thirty milligrams per kilogram per day for three to five days, the ciclosporin at two to seven milligrams per kilogram per day, and the anakinra at two to four milligrams per kilogram per day subcutaneously. The broad-spectrum antibiotics are given empirically for the presumed sepsis until the cultures are negative, because the sepsis and the MAS are indistinguishable at the onset and may coexist. [10][7]

The escalation if refractory

If the MAS does not respond to the glucocorticoids, the ciclosporin and the anakinra within the first few days, the anakinra is escalated to four to eight milligrams per kilogram per day. The etoposide at one hundred and fifty milligrams per square metre on the HLH-2004 protocol and or the emapalumab, the monoclonal antibody against the interferon-gamma, are considered for the refractory case. The child remains in the paediatric intensive care unit with the multidisciplinary team of the paediatric rheumatology, the haematology and the infectious diseases. [3][7]

Communication and the family

The family is counselled honestly on the macrophage activation syndrome, the rationale for the reduction of the tocilizumab, and the plan for the anakinra and the glucocorticoids. The parents are taught the warning signs of the persistent fever and the new bleeding and the need to present at once. The child is prepared in an age-appropriate way, and the multidisciplinary team is assembled around the family. The long-term plan includes the biologic optimisation after the resolution of the MAS, the infection surveillance, and the regular monitoring of the ferritin and the platelet trend. [9][10]