Reversed halo sign in acute schistosomiasis

1. Professor, Graduate Program in Health Sciences, Faculdade de Medicina de São José do Rio Preto – FAMERP, São José do Rio Preto School of Medicine – São José do Rio Preto, Brazil 2. Adjunct Professor, Faculdade de Medicina de São José do Rio Preto – FAMERP, São José do Rio Preto School of Medicine – São José do Rio Preto, Brazil 3. Physician, Ultra X, São José do Rio Preto, Brazil 4. Professor, Graduate Program in Radiology, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil; and Professor of Clinical Medicine, Petrópolis School of Medicine, Petrópolis, Brazil 5. Full Professor Emeritus, Fluminense Federal University, Niterói, Brazil; and Associate Professor, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil A 35-year-old rural worker presented with a 15-day history of progressive dyspnea, which, for the last 5 days, had been accompanied by dry cough, myalgia, asthenia, and fever. The patient also mentioned that he had swum in natural waters within the last 20 days. Physical examination showed mild painful hepatomegaly and splenomegaly. Chest X-rays showed bilateral reticulonodular infiltrates. An HRCT scan revealed patchy areas of ground-glass attenuation, irregular interlobular septal thickening, intralobular interstitial thickening, and small confluent nodules. Nodular reversed halos (focal, rounded areas of ground-glass opacity surrounded by more or less complete rings of consolidation) were also observed in the lower lobes of the lungs (Figure 1). Blood tests showed leukocytosis with eosinophilia. Bronchoalveolar lavage findings were negative. The patient underwent open lung biopsy. Histological examination of the biopsy sample demonstrated areas of parenchymal granulomatous inflammation, with clusters of epithelioid histiocytes, giant cells, and some eosinophils. In addition, those areas were surrounded by chronic inflammatory cell infiltrate and numerous schistosome ova (Figure 2). The final diagnosis was acute schistosomiasis. The patient was treated with thiabendazole and oxamniquine, showing improvement of the clinical and imaging findings over the following days. Another HRCT scan, obtained four months after treatment, showed no abnormalities. Schistosomiasis is a major helminthic infection in tropical and subtropical regions; it has affected an estimated 200 million people, resulting in considerable morbidity and occasional mortality.(1-3) In such regions, native populations and travelers are at risk of infection with Schistosoma spp.(2) The infection is acquired through direct contact with contaminated freshwater.(2) The spread of infection requires an intermediate host—freshwater snails specific to each Schistosoma species—whose geographic distribution limits the distribution of the parasite.(3) Humans are colonized by three major species of the parasite(1): S. mansoni, common in Africa, the Middle East, and South America; S. haematobium, common in Africa and the Middle East; and S. japonicum, common in Japan and China. Schistosomiasis progresses through three phases, as defined by the migration of the helminth: allergic (cercarial) dermatitis, which occurs during the penetration of cercariae into the skin; acute schistosomiasis, which occurs during the oviposition phase; and chronic schistosomiasis, caused by the formation of granulomas and fibrosis around the helminth eggs retained in the pulmonary vasculature, which can result in arteriolitis obliterans, pulmonary hypertension, and cor pulmonale.(1) Although the clinical presentation of acute schistosomiasis varies widely, most individuals are asymptomatic. Symptoms and signs can include fever, chills, weakness, weight loss, headache, nausea, vomiting, diarrhea, hepatomegaly, and splenomegaly. The disease is usually self-limited, but severe cases can result in death.(2,3) Marked eosinophilia can be present.(1-3)