Case Report: Definitive diagnosis of pulmonary parasitic infection via cytomorphology and histopathology in a patient with non-specific pulmonary nodules and hemoptysis after raw deer blood consumption.

BACKGROUND

Pulmonary parasitic infections are notorious "great masqueraders" in clinical practice, with presentations including hemoptysis and non-specific cavitary nodules that overlap extensively with common pulmonary diseases. Diagnostic challenges are exacerbated by unusual paratenic transmission routes and extensive serological cross-reactivity among trematodes.

CASE PRESENTATION: A 38-year-old male deer and dog breeder with raw deer blood consumption history presented with 2 months of cough and intermittent hemoptysis. Outside hospital chest CT revealed a right lower lobe (RLL) cavitary nodule, with initial lung biopsy only showing chronic inflammation. Laboratory workup identified progressive peripheral eosinophilia (up to 22.4%), massive eosinophilic pleural effusion (66% of nucleated cells) with extreme low pleural fluid glucose (0.10 mmol/L), and broad serological cross-reactivity (positive Clonorchis sinensis, Schistosoma japonicum, and Paragonimus westermani IgG) with normal hepatobiliary ultrasound. Expert pathological consultation of the initial biopsy slides identified parasitic ova within multinucleated giant cells, confirming the diagnosis. The patient was treated with praziquantel, with complete symptom resolution and radiological regression at 2.5-month follow-up.

CONCLUSION

Massive eosinophilic pleural effusion combined with extreme low pleural fluid glucose is a pathognomonic clue for pulmonary parasitic infection. Histopathology remains the diagnostic gold standard, while cytomorphology is indispensable for resolving serological ambiguity, underscoring the pivotal role of laboratory medicine in atypical parasitic infection diagnosis.