A 16-year-old girl presented with anal discharge of a white thread-like object. She denied additional symptoms. She had consumed raw salmon three weeks ago. Physical examination revealed no abnormal findings, and blood tests were unremarkable. However, abdominal ultrasound revealed a hyperechoic strand-like structure (Fig. 1). Stool examination revealed the presence of cestode ova. Therefore, she was admitted to our hospital and treated with oral praziquantel. A tapeworm, roughly 2.5 m long, was extracted from her feces (Fig. 2). Restriction fragment length polymorphism analysis with PCR-amplified cox1 gene fragment was performed,1 which identified the causative cestode was Diphyllobothrium nihonkaiense.

Fig. 1.

Longitudinal view of the rectum showing high echoic strand-like lesion (blue arrows). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

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Fig. 2.

The tapeworm unfolded after deworming with praziquantel.

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In Japan, D. nihonkaiense is the most common diphyllobothriasis-causing tapeworm.2 The diagnosis was based on the appearance after deworming, and the species was correctly identified using a molecular technique. The effectiveness of ultrasound has been reported in several publications.3,4 In cases such ours, ultrasound is useful for deciding whether to treat patients with praziquantel because the tapeworms are extracted naturally. In conclusion, abdominal ultrasonography can be useful for diagnosing diphyllobothriasis.