Pulmonary Dirofilariasis (PD) is an unusual infection manifesting as a solitary or multiple pulmonary nodules mimicking lung carcinoma. This is a case of PD detected incidentally in a patient with a history of stage 4 lymphoma in remission. We are aware of no prior reports describing an association between PD and lymphoma.
A 59 year old man with history of stage 4 diffuse large B cell lymphoma involving lungs and bone marrow currently in remission, presented for routine follow-up. The patient was asymptomatic from a pulmonary perspective. He denied fever, weight loss and other constitutional symptoms. Physical examination was normal. Surveillance chest CT showed bilateral pulmonary nodules. PET scan showed increased uptake in the corresponding areas. CBC showed mild eosinophilia and metabolic profile was normal. Serological tests for various infections were negative. Bone marrow biopsy was negative for marrow relapse of lymphoma. Lung biopsy showed extensive caseating granulomas with the necrotic areas ringed by palisaded histiocytes and scattered multinucleated giant cells. There were many scattered fragments of partially calcified material, some of it with ill-defined cylindrical shapes. The inner structure morphology was consistent with decaying fragments of Dirofilaria immitis. Elisa test for IgG4 antibody against filarial antigen was positive at 1: 16. Based on the clinicoradiological and pathological features, the diagnosis of pulmonary dirofilariasis was made.
Pulmonary dirofilariasis (PD) is a rare zoonotic disease in the United States. Most reported cases are from southeastern, eastern and south coastal states. Dashiell described first case of human pulmonary dirofilariasis (PD) infection due to Dirofilaria immitis (DI) in 1961 (1). PD is a rare entity caused by DI (the dog heart worm), a filarial nematode that is transmitted to humans by mosquitoes. From the subcutaneous tissue the worm travels to the heart and then enters the lungs. Humans are not suitable hosts for this worm, so the larva dies and antigens from the dead worm provoke endarteritis and a granulomatous response. Patients with PD are typically asymptomatic though occasionally they may present with cough, chest pain and hemoptysis. The most common presentation of PD is a solitary pulmonary nodule discovered on a chest radiograph (2). Rarely, PD may present as multiple pulmonary nodules simulating lung metastases. There are no characteristic clinical or radiological features to distinguish PD from the solitary / multiple pulmonary nodule(s) secondary to other causes like primary lung neoplasm, metastatic pulmonary lesions and various other granulmonatous lesions. Microscopically the nodules consist of coagulation necrosis and caseating granulomas with worms at various stages of disintegration. The diagnosis is generally made based on the histopathology. Serological tests may aid in the diagnosis. Serological titres by enzyme linked immunosorbent assay and indirect hemagglutination tests have good sensitivity early in the course of infection but sensitivity declines as the time interval between worm death and serological testing prolongs (3). As these organisms are dead, no specific anti dirofilarial treatment is indicated.
One should be aware of and consider pulmonary dirofilariasis in the differential diagnosis of solitary/multiple pulmonary nodules and granulomatous pulmonary lesions in the appropriate clinical and epidemiologic setting. No anti-helminthic treatment is required as this is the pathological response to the dead parasite.
Chandra Katikireddy, None.