Persistent Type B Hyperlactataemia as a Diagnostic Clue to Occult Diffuse Large B-cell Lymphoma-Associated...

Haemophagocytic lymphohistiocytosis (HLH) is a rare, life-threatening hyperinflammatory disorder characterised by excessive immune activation. It may be primary or secondary, with secondary HLH associated with a range of triggers; the most common are infections, autoimmune and autoinflammatory conditions, haematological malignancies and other immune‑dysregulatory states. We present a case of a man in his 70s who presented with a two-week history of exertional dyspnoea, profound fatigue and anorexia. Initial investigations demonstrated marked hyperferritinaemia, thrombocytopenia, mild anaemia, cholestatic liver dysfunction and disproportionately elevated lactate without acidosis. Despite intravenous fluids, lactate remained persistently elevated, consistent with type B hyperlactataemia. Computed tomography (CT) of the abdomen and pelvis demonstrated appearances suggestive of hepatitis but no organomegaly, significant lymphadenopathy or biliary obstruction. Despite empirical antibiotics and fluid resuscitation, he developed progressive pancytopenia, worsening liver dysfunction and rising lactate. Further investigations supported secondary HLH, with an HScore of 186, hypertriglyceridaemia and markedly elevated lactate dehydrogenase. Initial treatment with corticosteroids and anakinra resulted in limited response. An autoimmune trigger was initially considered given his Raynaud's phenomenon and ongoing connective tissue disease investigation. However, bone marrow biopsy subsequently confirmed diffuse large B-cell lymphoma (DLBCL). Reduced-dose rituximab, cyclophosphamide, doxorubicin, vincristine and prednisone/prednisolone (R-mini-CHOP) was commenced, resulting in the resolution of hyperlactataemia, normalisation of blood counts and liver function and improvement in performance status. PET-CT after two cycles demonstrated a complete metabolic response. This case highlights the importance of considering secondary HLH in patients with unexplained cytopenias, hyperferritinaemia, liver dysfunction and persistent hyperlactataemia. Persistent hyperlactataemia despite adequate fluid resuscitation should prompt the consideration of systemic causes beyond tissue hypoperfusion. Bone marrow biopsy is crucial for identifying occult malignancy when conventional imaging fails to show overt malignancy. The early recognition of HLH and investigation for an underlying aetiology may facilitate timely definitive treatment.