en Reumatology Reumatology case report case report <span style="font-family:Times New Roman;"><span style="font-size:14px;"><span style="color:#0000ff;"><strong><em>Background</em></strong><em>:</em></span> Abdominal pain is a routine symptom. Mesenteric arteritis, intestinal vasculitis, enteric vasculitis, mesenteric vasculitis, lupus peritonitis, and abdominal serositis are the possible differential diagnoses. Therefore, lupus enteritis has an uncertain outbreak.<br> <span style="color:#0000ff;"><strong><em>Case Presentation</em></strong><em>:</em></span> A 27-year-old woman presented with clinical presentation of peritonitis suggestive of acute abdominal crisis with three days history of fever, bloody diarrhea, nausea, vomiting and seizure. Further work up revealed microangiopathic hemolytic anemia, thrombocytopenia, proteinuria, polyserositis and her initial autoimmune panel all were negative. Since SLE was at the top of our diagnosis, we considered glucocorticoid and cyclophosphamide pulse therapy. After approximately two months of her initial presentation, when all of her symptoms subsided by initial therapy, her antinuclear antibody became positive at 1:320 titers and renal biopsy was compatible with lupus nephritis (stage III).<br> <span style="color:#0000ff;"><strong><em>Conclusion</em></strong><em>:</em></span> It is crucial to take the diagnosis of lupus into consideration, in case of any young female with multiorgan involvement even without positive antibody tests. As in this case, it took more than two months after initial presentation to confirm the diagnosis via renal biopsy and only after then, serum autoantibodies became seropositive</span></span> Systemic lupus erythematosus, lupus nephritis, cyclophosphamide therapy. 482 486 http://caspjim.com/browse.php?a_code=A-10-1402-1&slc_lang=en&sid=1 Samira Alesaeidi alesaeidi@sina.tums.ac.ir 100319475328460031266 100319475328460031266 No 1. Department of Internal Medicine, Rheumatology Research Center, Tehran University of Medical Sciences, Tehran, Iran Morteza Daraei mortezadaraie@gmail.com 100319475328460031267 100319475328460031267 No Department of Internal Medicine, Imam khomeini Hospital, Tehran University of Medical Sciences, Tehran, Iran Amir Salami khanshan Amir.slm1990@gmail.com 100319475328460031268 100319475328460031268 No Student Research Committee, Faculty of Medicine, Iran University of Medical Sciences, Tehran, Iran Hamed Zainaldain ahmad.23088@gmail.com 100319475328460031269 100319475328460031269 Yes School of Medicine, Tehran University of Medical Sciences, Tehran, Iran.