Pediatric emergency medicine trisk 2999 2999
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MAS, sometimes known as reactive HLH, can be thought of as HLH in the setting of
autoimmune disease, most commonly sJIA and adult-onset Still disease. This serious
complication may occur in as many as 30% to 50% of children with sJIA. Children
with SLE and other autoimmune disorders are also at risk for MAS, and vigilance for
its evolution is advised when such children present with fever and marked laboratory
and examination abnormalities. It is often challenging to differentiate a flare of
underlying disease or superimposed systemic infection from MAS, and these
pathologic entities may also coexist.
Clinical Considerations
The diagnosis of either HLH or MAS should be considered in an ill child with
prolonged fever, HSM, elevated inflammatory markers, hematologic cytopenias,
coagulopathy, neurologic symptoms, and/or evidence of liver dysfunction. A
significantly elevated ferritin is a sensitive and specific marker of these processes, with
ferritin levels of >500 raising clinical concern. As hyperferritinemia increases (1000 to
10,000s range), the level of clinical suspicion rises. If HLH or MAS is suspected,
additional evaluation for hypertriglyceridemia and hypofibrinogenemia should be done.
Immune assays that are more specific for HLH/MAS, including evaluation of NK cell
numbers and function, as measured in a cytotoxicity assay, can assist in identifying this
disorder, though the results of these studies are often delayed. Flow cytometric
measurement of perforin, soluble CD25 (soluble IL-2 receptor alpha), and soluble
CD107a expression may be helpful in making the diagnosis; though once again, these
results are not usually available to the ED physician. The criteria for the diagnosis of
HLH have been formalized ( Table 101.14 ). The diagnosis of MAS can be made in the
appropriate clinical setting even when HLH 2004 criteria are not met. Recently, clinical
criteria for the diagnosis of MAS have been validated, however, they are not yet widely
used.
