Metastatic Crohn's Disease and Acute Myeloid Leukemia: A Diagnostic Paradox in a Severe Hyperinflammatory State.

Crohn's disease (CD) is a chronic immune-mediated inflammatory disorder in which extraintestinal manifestations occur in up to 40% of patients. Metastatic Crohn's disease (MCD), characterized by noncaseating cutaneous granulomas anatomically remote from the gastrointestinal tract, is among the rarest of these manifestations. Its coexistence with occult acute myeloid leukemia (AML) and secondary hemophagocytic lymphohistiocytosis (sHLH) in a treatment-naïve patient constitutes an exceptional clinical triad with profound diagnostic and therapeutic implications. We report a 56-year-old woman without prior immunosuppressive exposure who presented with severe panenteric CD, MCD manifesting as necrotic lower-extremity nodules, and a submandibular abscess. Profound bicytopenia (hemoglobin: 5.3 g/dL, reference range: 13-18 g/dL; platelets: 12,000/μL, reference range: 150,000-450,000/μL) prompted a bone marrow evaluation, which revealed hypercellularity with 9% myeloid blasts (CD34+, CD117+). Although these findings required an urgent repeat marrow evaluation, cytogenetic/molecular testing, and hematology clearance due to the high risk of an indeterminate or pre-leukemic state, the presence of active, refractory gastrointestinal bleeding prompted the immediate initiation of infliximab induction. Given the absence of prior therapy and the presence of marked systemic inflammation, including concurrent pneumonia and active CD, these findings were initially attributed to reactive myelodysplastic mimicry. However, while systemic inflammation from pneumonia and active CD can mimic myelodysplasia, a 9% blast count with severe cytopenias should not be safely dismissed as merely reactive. Within days of the first infliximab infusion, the patient developed explosive leukocytosis (40,000/μL). Repeat flow cytometry demonstrated 37% immature myeloid blasts (CD34+, CD117++, HLA-DR+, CD123+), establishing a diagnosis of AML without maturation (FAB M1). Concurrently, overt hemophagocytosis with extreme hyperferritinemia confirmed concomitant sHLH (HScore: 227). This case highlights a critical and underrecognized risk: TNF-α may act as an endogenous immunological brake against clonal expansion. In our patient, TNF-alpha blockade may have contributed to the loss of immune control over an occult myeloid clone, dismantling this surveillance mechanism and precipitating a rapid transition to fulminant leukemia while triggering sHLH. Although causality cannot be proven from this single case and a direct triggering effect by infliximab remains speculative unless other potential triggers are thoroughly evaluated, the temporal association is striking. Severe systemic inflammation can create a reactive bone marrow phenotype indistinguishable from early myeloid neoplasia or myelodysplastic syndrome, posing a life-threatening diagnostic trap. Comprehensive hematologic evaluation-including repeat bone marrow assessment under controlled inflammatory conditions-should be considered mandatory before initiating biologic therapy in patients with CD and unexplained cytopenias or borderline blast counts.