We present a rare case of mirror syndrome due to anti-Kpa antibodies, which can be difficult to identify with routine screening tests.

CAR-T cell related HLH/MAS is an unusual manifestation of severe cytokine release syndrome (CRS) with high mortality rates and a challenging diagnosis. The establishment of specific diagnosis criteria is essential, and the combination of several techniques for CAR-T cell follow-up, allows a more precise management of this complication.