Pleural Fluid Homing by Anaplastic Large Cell Lymphoma-Cytopathologic Diagnosis of a Rare Presentation

Anaplastic large cell lymphoma (ALCL) is a rare and aggressive subtype of non-Hodgkin lymphoma characterised by large, anaplastic lymphoid cells with strong CD30 expression. Although ALCL commonly presents with nodal and extranodal involvement, pleural effusion as an initial manifestation is exceedingly uncommon. Pleural fluid involvement generally indicates advanced disease, often resulting from direct pleural infiltration or systemic dissemination, and is associated with a poor prognosis.

We report the case of a 21-year-old female who presented with fever, abdominal pain, breathlessness, and significant weight loss. Clinical evaluation revealed generalized lymphadenopathy and a left-sided pleural effusion. Cytologic examination of the pleural fluid showed dispersed large atypical lymphoid cells with irregular nuclear contours, prominent nucleoli, and abundant vacuolated cytoplasm. Immunocytochemistry on the cell block demonstrated strong CD30 and ALK positivity, confirming the diagnosis of ALK-positive ALCL, which was subsequently corroborated by inguinal lymph node biopsy.

The patient was promptly started on CHOP chemotherapy. Despite early initiation of treatment, her condition rapidly deteriorated, and she succumbed to the disease within 2 weeks of diagnosis, reflecting the fulminant nature of effusion-positive ALCL.

This case highlights the diagnostic value of effusion cytology combined with cell block immunocytochemistry in establishing a definitive diagnosis of ALCL from pleural fluid, even in the absence of an overt mass lesion. Early recognition of this rare presentation is critical for timely management, as effusion-dominant ALCL may portend an aggressive clinical course.