Purulent Peritonitis Masked by Disease-Modifying Therapy: A Case Report

Common MS treatments, particularly disease-modifying therapies (DMTs), can influence immune responses and potentially mask infections, even when laboratory findings appear normal 8 .Among these drugs is dimethyl fumarate (DMF), used for relapsing remitting multiple sclerosis (RR-MS).Although its mechanism of action is not fully understood, studies show a dose-dependent effect of DMF on T-cell counts which occurs through the induction of apoptosis and decreased proliferation of CD4 + and CD8 + T-cells 9 .When looking at the intestinal barrier and gut-associated lymphoid tissue (GALT) we must consider the role of lymphocytes and the effect of lymphocytopenia.When bacteria breach the gastrointestinal epithelial layer, the body triggers an adaptive immune response by activating CD4 + T-cells and inducing cytokine release; therefore lymphocytopenia could impair the intestinal barrier and facilitate the transit of bacteria from the intestines into the peritoneal cavity 10 .Here, we report the case of an atypical presentation of purulent peritonitis and abdominal abscess in a 60-year-old female with RR-MS undergoing therapy with DMF. Key Clinical Message:Dimethyl fumarate-induced lymphocytopenia may obscure typical laboratory signs of severe intra-abdominal infection.Multiple sclerosis patients on disease-modifying therapy can present atypically despite severe pathology.Maintain a low threshold for early imaging and surgical evaluation when acute abdominal symptoms arise to prevent delayed diagnosis and sepsis.