BACKGROUND: The gastrointestinal tract is a rare site for extramedullary involvement in acute promyelocytic leukemia (APL).

CASE REPORT: A 43-year-old female with no past medical history presented complaining of mild abdominal pain, fever, and chills for the past day. On examination, she was tachycardic and febrile, with mild tenderness of her right lower quadrant and without signs of peritoneal irritation. Laboratory examination revealed pancytopenia and DIC, with a fibrinogen level of 290 mg/dL. CT of the abdomen showed a thickened and hyperemic appendix without perforation or abscess, compatible with acute appendicitis. The patient was given IV broad-spectrum antibiotics and was transfused with packed red blood cells and platelets. She underwent uncomplicated laparoscopic appendectomy and bone marrow biopsy, which revealed neoplastic cells of 90% of the total bone marrow cellularity. Flow cytometry indicated presence of 92.4% of immature myeloid cells with t (15: 17) and q (22: 12) mutations, and FISH analysis for PML-RARA demonstrated a long-form fusion transcript, positive for APL. Appendix pathology described leukemic infiltration with co-expression of myeloperoxidase and CD68, consistent with myeloid sarcoma of the appendix. The patient completed a course of daunorubicin, cytarabine, and all trans-retinoic acid. Repeat bone marrow biopsy demonstrated complete remission. She will follow up with her primary care physician and hematologist/oncologist.

CONCLUSIONS: Myeloid sarcoma of the appendix in the setting of APL is very rare and it might play a role in the development of acute appendicitis. Urgent management, including bone marrow biopsy for definitive diagnosis and urgent surgical intervention, dramatically improve prognosis.

Keywords: Appendectomy - methods, Appendicitis - surgery, Appendix - surgery, Diagnosis, Differential, Laparoscopy, Leukemia, Promyelocytic, Acute - complications, Leukemic Infiltration - pathology, Tomography, X-Ray Computed