A 44-year-old woman who had no history of tuberculosis was referred to our hospital because of lower abdominal pain and ascites. Blood tests revealed an elevated CA125 level (326 U/mL), and enhanced computed tomography detected thickened peritoneum and enhanced peritoneal nodules. While microbiologic testing and cytologic examination of ascites were negative, the T-SPOT®.TB test was positive. Diagnostic laparoscopy was conducted, revealing tiny nodular lesions on the peritoneal surfaces. Pathological examinations showed granuloma and Langhans giant cells with caseous necrosis; however, no signs of malignancy were observed. After administering a combination drug regimen using isoniazid, rifampicin, pyrazinamide, and ethambutol, she had been on a good clinical course. Tuberculous peritonitis (TBP) is one of the types of extra-pulmonary tuberculosis. Although early diagnosis is known to improve patients' prognosis, it is still difficult to obtain due to the non-specificity of symptoms. A number of reports already revealed that laboratory tests such as tumor marker show similar results with carcinomatous peritonitis. Detecting Mycobacterium tuberculosis is the gold standard for diagnosis, but this detection is difficult in routine practice because of the low detection rate. Auxiliary tests such as radiography, immunological test, and laparoscopy are usually conducted. Laparoscopic surgery is the most common method for early diagnosis, detection of localization of infection, and differentiation from carcinomatous peritonitis. As the long-term treatment is necessary for TBP, confirming other diseases requiring uncomplicated treatment is important.
