An unusual case of paediatric plasmablastic lymphoma presenting with malignant effusion and the challenges in its diagnosis.

Plasmablastic lymphoma (PBL) is an aggressive non-Hodgkin lymphoma occurring commonly in the oral mucosa and jaw of human immunodeficiency virus (HIV) positive adult males. PBL is not a common occurrence in children and a presentation with malignant effusion is rarely reported. Herein, we share our experience in the challenges confronted in the diagnosis of PBL in a 6-year-old, HIV positive boy presenting with malignant pleural and peritoneal effusions along with gum hypertrophy, lymphadenopathy and paranasal sinus mass. Amenability of pleural effusion to exfoliative cytology led to an initial cytological examination demonstrating large atypical lymphoid cells with plasmacytoid morphology and a plasmablastic variant of Burkitt lymphoma was initially considered. However immunophenotyping by flowcytometry (FCM) and a cell block immunohistochemical evaluation of the serous effusion suggested a plasma cell immunophenotype and a diagnosis of PBL was favored. A subsequent biopsy from the paranasal sinus mass confirmed the diagnosis of PBL but showed tumour cell angiocentricity on morphology and CD45 expression on immunohistochemistry (IHC), both unusual features in PBL. A CD20 negative/MUM-1 positive immunoprofile and presence of a solid tumour mass in a typical location in addition to malignant effusion substantiated the diagnosis of PBL. The patient was offered HAART (highly active antiretroviral therapy) and chemotherapy and is on follow-up. Paediatric PBL with malignant effusion is rarely reported and this case stresses the importance of use of a multimodality diagnostic approach for an accurate diagnosis.