How do you approach relapsed idiopathic HLH?

This question is quite non-specific - the answer depends very much on the specific context (child, adult, relapsed after what treatment?) and as such, can only be answered in broad strokes.

First, ensure that it is truly idiopathic – check EBV, CMV viral loads, and other viral/infectious triggers as ...

If the patient was previously in remission after etoposide and steroids, they may well respond to etoposide and steroids again. I strongly consider hematopoietic stem cell transplant in anyone who relapses after an episode of HLH, since it is usually a harbinger of recurrent and potentially life-thr...