A 20-year-old male patient was admitted to our hospital with abdominal pain in the epigastric region, weight loss, and fever for 2 months. He had low back pain for 6 months and was evaluated for this complaint in another hospital. He had significant weight loss of 10 kg in 2 months and fever especially at nights. Past or family history revealed no signs of chronic or significant illnesses. Physical examination was normal. X-ray chest was normal. Anteroposterior plain radiograph of the sacroiliac joints revealed grade II bilateral sacroiliitis. Human leukocyte antigen B27 was positive. Liver and kidney function tests were normal. Lactic acid dehydrogenase was 229 U/L, upper of normal limits. Hemoglobin was 9.6 gm/dL; the patient had iron deficiency anemia. Serum angiotensin-converting enzyme level was 10.7 U/L (normal 8.0-52). His human immunodeficiency virus status was negative. F-18 FDG PET/ CT revealed multiple hypermetabolic malignant lymphadenopathies at gastrohepatic, gastrosplenic, celiac, superior mesenteric, peripancreatic and hepatobiliary region, and paragastric region in size as 18 × 15 mm (SUVmax: 12.3) and diffuse gastric wall thickening as linitis plastica (SUVmax: 13.3), multiple hypermetabolic peritoneal implants in the omentum (SUVmax: 5.7) and peritoneum, and mild hypermetabolic suspected malignant lymph nodes at left supraclavicular region (). Gastric ulcer at incisura angularis was detected on upper GI endoscopy (). Endoscopic biopsies were repeated for histopathological and microbiological differential diagnosis. Histopathological examination showed granulomatous gastritis, Langhans-type giant cells, granulomas composed of epithelioid histiocytes, ulceration, and exudates in the two samples. Real-time TB-PCR were negative, Erlich-Ziehl-Neelsen staining bacteria were negative. Gastric fluid examination revealed Gram-positive cocci, Gram-positive bacillus, and no leukocytes. Exploratory laparotomy was done to sample the biggest sized lymph nodes for tissue diagnosis and explore the peritoneum for TB infection, lymphoma, and Crohn’s disease to make differential diagnosis. During laparotomy, the abdomen and peritoneum were intact and normal; two lymph nodes were extracted for histopathological and microbiologic diagnosis. Histopathology of the lymph nodes extracted by exploratory laparotomy revealed granulamatous lymphadenitis with granulomas including giant cells, mostly suspecting TB (). Ankylosing spondylitis was also diagnosed. Bath ankylosing spondylitis disease activity index score was 1.0, disease activity was low. Patient was put on ATT consisting of (2HREZ/7HR) regimen as isoniazid, rifampicin, ethambutol, and pyrazinamide at therapeutic doses for initial 2 months followed by rifampicin and isoniazide in the same doses for the last 7 months. At the 6th week of treatment, he gained weight about 6 kg and he was feeling healthy. Hemoglobin was 12.6 gm/dL. We performed follow-up F-18 FDG PET/ CT. The F-18 FDG PET/ CT images (maximum intensity projection, CT, and fusion PET/ CT) exhibited a complete response to ATT with no residual disease (). We have taken written informed consent from the patient reported in this study.