Macrophage Activation Syndrome in a Patient with Systemic Juvenile Idiopathic Arthritis: Complexities of the Diagnosis

Background: Macrophage activation syndrome (MAS) is the most dangerous complication of systemic juvenile idiopathic arthritis (sJIA).

The objective of this study was to present the challenges of MAS diagnosis in patients with sJIA.

Case presentation: A 3-year-old boy was admitted to the hospital with complaints of fever up to 40.5° C, single vomiting and limping. Laboratory testing revealed anemia, leukocytosis 25,600/µl, an ESR of 28 mm/hr, C-reactive protein 26.8 mg/dL. Antibiotic therapy was prescribed. A day later erythematous macular rash on the back, chest and right elbow appeared.

The rash was considered as a medication allergic reaction and intravenous prednisolone was prescribed. Despite the treatment the patient continued to be febrile, and a transient abdominal pain occurred; therefore, leukemia was decided to be excluded and prednisolone was rapidly interrupted for one day.

On the second day after prednisolone interruption, generalized tonic-clonic seizures with a loss of consciousness and coma over the next 3 days developed. Acute encephalitis was suspected. Herpes viruses and Lyme borreliosis were ruled out. Increased levels of LDG, ALT, AST and ferritin (1389 ng/ml) were detected. Intravenous methylprednisolone (10 mg/kg/day for 5 days), and intravenous immunoglobulins were prescribed. On the background of the pulse therapy the temperature normalized, the rash disappeared.

Enlarged cervical lymph nodes, transient elbow swelling, hepatosplenomegaly, tachycardia and severe sluggishness were revealed. Rheumatoid factor and antinuclear antibodies were negative. Taking into account quotidian fever, transient erythematous rash, lymphadenopathy, arthritis and arthralgia, hepatosplenomegaly sJIA was diagnosed. Oral methylprednisolone was continued. Considering involvement of the nervous system and high ferritin level, increased AST and fibrinogen values 313 mg/dl MAS was diagnosed according to the 2016 Classification criteria for MAS.

Conclusion: The lack of specific symptoms of sJIA and MAS leads to the diagnostic challenges and requires exclusion of infections, malignancies and other conditions with similar signs.