An incidental finding of severe hyperferritinaemia: a lesson to be learned.

Haemophagocytic lymphohistiocytosis is a rare, under-recognised and often misdiagnosed condition, characterised by a hyperinflammatory response to malignancy or infection. In this case, the cause was a bone marrow isolated anaplastic large cell lymphoma without radiological evidence of systemic disease, a phenomenon rarely described. We present the case of a previously fit and well 64-year-old female who presented on multiple occasions to primary and secondary care in a stable condition with an undifferentiated illness with the only consistent feature being a marked, unexplained hyperferritinaemia. The history highlights the importance of ferritin as a marker of phagocytic activity and how severely high levels, even in the well patient, should prompt early bone marrow biopsy. The prognosis of haemophagocytic lymphohistiocytosis is invariably poor as the condition is usually secondary to a serious underlying disease such as haematological malignancy as in this case. The diagnostic difficulty often leads to delayed recognition and treatment.