Forme Fruste of HLH (haemophagocytic lymphohistiocytosis): diagnostic and therapeutic challenges.

Infants and young children often present with a persistent febrile episode, sick appearance and negative infectious disease work-up. These patients present serious diagnostic and therapeutic problems to those who provide medical care, particularly since these children are clinically sick. We present a 13 month old child who presented with this clinical challenge. She was ultimately thought to have an incomplete form of HLH with underlying pathophysiology of hypercytokinemia, but also could have been a case of incomplete form of Kawasaki disease. She responded to IVIG, but this does not differentiate one diagnosis from another. Unfortunately we failed to obtain tests to exclude genetic etiologies of HLH, which would be important for predicting severity and risks of future recurrence. We wish to present this case so that one should do a thorough work up to establish a firm diagnosis of HLH and to search for genetic causes of this disorder. 2015 BMJ Publishing Group Ltd.