Patient selection: pediatric patient with systemic juvenile idiopathic arthritis (SJIA)
Finding categories:
(1) clinical
(2) laboratory
(3) bone marrow histopathology
Clinical findings:
(1) central nervous system dysfunction with irritability, disorientation, lethargy, headache, seizures and/or coma
(2) bleeding disorder, with purpura, easy bruisability, and/or mucosal bleeding
(3) hepatomegaly with liver >= 3 cm below the right costal margin
Laboratory findings:
(1) decreased platelet count (<= 262,000 per µL)
(2) elevated serum AST (> 59 IU/L, where the normal upper limit of the reference range in pediatric patients is 40 IU/L according to Table III; 59 would be approximately 1.5 times the upper limit of normal)
(3) leukopenia (<= 4,000 per µL)
(4) hypofibrinogenemia (<= 250 mg/dL)
Bone marrow histopathology:
(1) macrophage hemophagocytosis
Diagnosis of MAS requires one or more of the following:
(1) >= 2 laboratory findings (out of 4)
(2) >= 2 clinical and laboratory findings (out of a total of 7)
(3) A bone marrow aspirate is only required in doubtful cases. I would think that its presence would be diagnostic by itself.
Performance:
• The laboratory only cutoff showed a sensitivity of 100% and specificity of 97%.
• The clinical and laboratory cutoff showed a sensitivity of 100% and specificity of 95%.
Limitations:
• The only finding that appears to be somewhat specific is the presence of macrophage hematophagocytosis in the bone marrow biopsy. Many of the findings reflect DIC or hepatitis.
• The designation of systemic juvenile idiopathic arthritis may represent a failure to identify a cause for a systemic arthritis.
• The thresholds for the laboratory findings are not fixed ("provided by way of example only").
• Clinical findings tend to appear late in the course. Laboratory findings are more useful for identifying cases early in the course of disease.
Other findings that may be seen in MAS in SJIA:
(1) high fever (>= 38°C)
(2) splenomegaly
(3) generalized lymphadenopathy
(4) paradoxical improvement in joint findings
(5) fall in ESR
(6) elevated serum ALT and LDH
(7) hyperbilirubinemia
(8) presence of fibrin degradation products
(9) hyponatremia
(10) hypoalbuminemia
(11) hyperferritinemia (ferritin is an acute phase reactant)
