[When cognitive biases lead to diagnostic errors].

A 62-year old patient with a severe case of hemophagocytic lymphohistiocytosis (HLH) was directly transferred to a hemato-oncological ward for inpatient diagnosis and potential treatment of a presumed lymphoproliferative disorder (LPD), although there was no clear evidence for the presence of a LPD. A serum PCR revealed visceral leishmaniasis as the actual HLH-trigger. Beforehand, several near-miss incidents occurred during initial patient management (diagnostics and treatment) due to cognitive biases among the team of physicians. Our case demonstrates the importance of careful clinical reasoning and awareness of cognitive biases in complex and rare diseases, particularly before performing invasive diagnostics and initiating treatment.