Lymphocyte-Predominant Ascites as a Clue to Peritoneal Tuberculosis: Two Case Reports and a Literature Review

Peritoneal tuberculosis (PTB) is difficult to diagnose because its clinical and imaging features are nonspecific and may mimic peritoneal malignancy or other intra-abdominal diseases. In addition, microbiological and molecular tests of ascitic fluid may be negative in paucibacillary disease.

We report two patients with PTB whose initial diagnostic evaluation was inconclusive. Both presented with abdominal distension and imaging findings suspicious for alternative diagnoses. In Case 1, acid-fast bacilli (AFB) staining and Mycobacterium tuberculosis (M. tuberculosis) nucleic acid amplification test (NAAT) of ascitic fluid were negative; targeted next-generation sequencing (tNGS) was not performed. Ascitic fluid cytology showed a nucleated cell count of 7900 ×10⁶/L, with 76% lymphocytes, mesothelial cells less than 1%, and no malignant cells. The patient improved after empiric treatment, and the diagnosis was later confirmed by positive ascitic fluid culture for M. tuberculosis. In Case 2, AFB staining and tNGS performed on pleural and ascitic fluid samples did not detect M. tuberculosis or other pathogens. Ascitic fluid cytology showed a nucleated cell count of 6,726 ×10⁶/L, with 82% lymphocytes, mesothelial cells less than 1%, and no atypical cells. PTB was ultimately confirmed by laparoscopic biopsy with histopathology and positive tissue AFB staining.

In the appropriate clinical setting, lymphocyte-predominant ascitic fluid with a low mesothelial cell proportion may provide a useful supportive clue to PTB when initial tests are negative or nondiagnostic. However, these cytological findings are nonspecific and should be interpreted together with clinical, microbiological, and histopathological findings.