Answer

Right-sided pleural effusion-Cause filariasis

Filariasis is a major public health problem in India with heavily endemic areas being Uttar Pradesh, Bihar, Andhra Pradesh, Orissa, Tamil Nadu, Gujarat, and Kerala. Wuchereria bancrofti is the most widespread of filarial organisms infecting humans. The major clinical presentations include fever, asymptomatic microfilariaemia, lymphatic obstruction, and tropical pulmonary eosinophilia. ^[1] Acute manifestations are fever, adenolymphangitis, funiculitis, epididymitis, and orchitis. Lymphedema, hydrocele, elephantiasis, and chyluria are features of chronic filariasis. ^[2] Tropical pulmonary eosinophilia is a form of occult filariasis causing interstitial lung disease due to immunologic hypersensitivity to filarial antigen. The adult worm resides in lymphatic vessels, whereas microfilariae, the larval forms, circulate in the peripheral blood. ^[3] Microfilariae probably appear in tissue fluids and exfoliated surface material due to lymphatic or vascular obstruction. Diagnosis is made on demonstrating microfilaria in blood samples and body fluids.

The development of pleural effusion is a rare manifestation of filariasis and such effusions are usually exudative in nature. ^[3] It may be due to lymphangitis, resulting in incomplete obstruction of lymphatics. Some others have also reported about pleural effusions due to filariasis. ^{[2],[4],[5],[6],[7]} In one case, microfilariae of Mansonella perstans[2] were detected, whereas in others, W. bancrofti were present. Four of these cases were from nonendemic areas. ^[2] Three cases had tropical pulmonary eosinophilia, whereas one did not have peripheral eosinophilia. ^[4] In another case, filarial larvae were detected on pleural biopsy. ^[2] Four of these showed a left-sided pleural effusion. ^[2],[6] The fluid was an exudate without eosinophilia. Reasons for exclusive left-sided effusion are not known. Only one case had tropical pulmonary eosinophilia with a bilateral transudative effusion. ^[5]

In India, where filariasis is endemic and the commonest cause of pleural effusion is tuberculosis, the coexistence of filariasis with pleural effusion is thought to be coincidental rather than etiologic. In our case, to rule out incidental parasitic occurrence, we made several wet films from the sediments of the fluid, which revealed numerous motile larvae. Smears showed microfilariae of W. bancrofti at four different occasions based on the morphology.

This case highlights the need for continued clinical vigilance when a diagnosed case of exudative pleural effusion does not behave in a manner it should on receiving ATT in an area with high prevalence of tuberculosis. Ruling out malignancy is also of prime importance. On ruling out malignancy, other causes, such as parasitic, collagen vascular disease, pancreatitis, or sarcoidosis, should be considered and a full microbiological workup should be pursued. Communication with microbiology staff is essential in the diagnostic process, which results in prompt institution of appropriate chemotherapy.

Our patient was started on diethyl carbamazine and she responded excellently. She was given treatment for 3 months and followed-up for 1 year with no evidence of refilling or recurrent effusion [Figure 3]. The presence of microfilariae in the pleural fluid and the successful response to treatment with diethylcarbamazine is strong evidence of filarial etiology of pleural effusion.

Figure 3 :Chest radiograph after 12 months Click here to view