Warthin-Finkeldey giant cells

Warthin-Finkeldey giant cells are multinucleated syncytial giant cells that form when measles virus (a paramyxovirus) causes fusion of infected cells, particularly in lymphoid tissue such as tonsils, lymph nodes, and appendix, as well as in the skin and respiratory epithelium during the prodromal and early rash phases of infection. Pathophysiologically, the measles virus fusion (F) protein mediates cell-to-cell fusion of infected cells, creating large syncytia with numerous nuclei (sometimes 100+) that contain eosinophilic intranuclear and intracytoplasmic inclusion bodies representing viral nucleocapsid aggregates. These giant cells are a hallmark histopathologic finding and are considered pathognomonic for measles infection, distinguishing it from other viral exanthems. Clinically, measles presents with the classic prodrome of cough, coryza, conjunctivitis (the three C's), followed by Koplik spots (pathognomonic enanthem on buccal mucosa) and a cephalocaudal maculopapular rash. Warthin-Finkeldey cells can be identified on biopsy of lymphoid tissue during this illness, though this is rarely required for diagnosis, which is typically made clinically or via serology/PCR. Rarely, in cases of subacute sclerosing panencephalitis (SSPE), a delayed complication of measles infection occurring years after the acute illness due to persistent CNS infection with a mutant measles virus, giant cells and inclusions may also be seen in neural tissue, though this is a distinct pathological entity in the brain rather than lymphoid tissue. Understanding this finding is important for boards as it links viral pathogenesis (cell fusion mechanisms) with classic histopathology, and measles remains a testable topic given its public health relevance and vaccine-preventable nature.