Macrophage Activation Syndrome in Childhood Lupus: A Paediatric Emergency

Macrophage activation syndrome (MAS) is a severe, potentially fatal complication of paediatric rheumatic diseases in which the immune system becomes hyperactivated: macrophages and T cells drive a runaway inflammatory cascade with very high fever, falling blood counts, liver involvement and coagulation abnormalities. It occurs most often in systemic juvenile idiopathic arthritis, but in childhood systemic lupus erythematosus it is a well-recognised and dangerous complication — and one that can develop in a child who appears to have "just a lupus flare". Because early treatment saves lives, recognition is the critical skill. This guide follows the Chinese expert consensus on diagnosis and treatment of MAS in paediatric rheumatic disease, childhood SLE section.

Recognising it

The signature is a child with known or suspected lupus who becomes acutely and persistently unwell, usually with high spiking fever that does not settle, and whose lupus activity markers and clinical state deteriorate together. Look for: enlargement of the liver, spleen or lymph nodes; a rash that may change character; falling blood counts affecting at least two of the three lines; liver enzyme rises; jaundice; bleeding or bruising from coagulation disturbance; and neurological changes — irritability, seizures or altered consciousness — which indicate central nervous system involvement and a worse prognosis. A paradox worth knowing: in MAS, the erythrocyte sedimentation rate may fall rather than rise, because fibrinogen is being consumed — a falling ESR in a seemingly deteriorating child is a warning, not reassurance.

Tests that identify it

The core laboratory pattern is a markedly elevated ferritin — often in the thousands, and rising ferritin is one of the most useful serial markers — combined with cytopenia, raised liver enzymes, low fibrinogen and high triglycerides. Coagulation studies show prolonged PT and APTT with low fibrinogen and elevated D-dimer. Bone marrow examination may show haemophagocytosis, though its absence does not exclude the diagnosis. Assessment for infection is mandatory before immunosuppression is intensified, because infection can trigger MAS and the two are otherwise difficult to separate; blood cultures, viral studies including EBV and cytomegalovirus, and appropriate imaging form part of the work-up.

Treatment

Treatment must be started promptly rather than after certainty is reached. First-line is high-dose corticosteroid: intravenous methylprednisolone pulse at roughly 15–30 mg/kg/day — generally capped at 1 g per day — for three to five days, repeated according to response, followed by oral prednisone-equivalent maintenance at around 1.5–2 mg/kg/day (commonly capped at 60 mg/day) with gradual tapering. Ciclosporin is added, typically at 4–6 mg/kg/day in two divided doses, and is particularly effective for the neurological and coagulopathic features. Where MAS is triggered by underlying lupus activity, treatment of the lupus itself is intensified at the same time. Refractory cases are treated with etoposide-based regimens or biologics targeting IL-1 or IL-6, and severe or recurrent cases are discussed for haematopoietic stem cell transplantation.

Supportive care and follow-up

Supportive treatment is as important as immunosuppression: correction of coagulopathy with plasma or fibrinogen, blood product support, infection surveillance and antibiotics, liver and kidney support, and intensive care monitoring. Once the acute episode resolves, immunosuppression is tapered slowly, with ferritin, blood counts, fibrinogen and liver function tracked to detect relapse — MAS recurs, and recurrence is more likely in children with underlying genetic predisposition, which should prompt consideration of genetic testing.

What parents should watch for

Fever that persists despite treatment, unusual pallor or bruising, jaundice, abdominal distension, or any change in behaviour or consciousness in a child with lupus should trigger an immediate call to the treating team rather than a wait-and-see approach. Ask your team specifically about ferritin monitoring during flares — a simple blood test that often identifies MAS before it becomes obvious.