A 32-year-old Indian woman presents with a 2-week history of easy bruising, petechiae, and gum bleeding. Blood smear shows 85% blasts with Auer rods. Which is the most common site of extramedullary involvement in acute myeloid leukemia?

Explanation

## Extramedullary Involvement in AML **Key Point:** Spleen and liver are the most common sites of extramedullary involvement in AML, occurring in 40–50% of cases at presentation. Hepatosplenomegaly is a frequent clinical finding and is part of the standard staging workup. ### Frequency of Extramedullary Sites in AML | Site | Frequency | Clinical Significance | |---|---|---| | Spleen and liver | 40–50% | Most common; part of staging | | Gingival infiltration | 20–30% (especially AML-M5) | Monocytic differentiation | | CNS involvement | 5–10% (at diagnosis); 30% (at relapse) | Poor prognosis; requires prophylaxis | | Skin (leukemia cutis) | 3–5% | Myeloid sarcoma; monocytic subtypes | | Bone | 2–3% | Rare; may cause bone pain | | Lymph nodes | 5–10% | Less common than in ALL | **High-Yield:** Gingival infiltration (gum hypertrophy, bleeding) is particularly common in **monocytic AML (AML-M5)** and is a clinical clue to the diagnosis. The presence of Auer rods on blood smear (as in this case) confirms AML and rules out ALL. ### Myeloid Sarcoma (Granulocytic Sarcoma) - **Definition:** Extramedullary tumor of AML blasts, also called "chloroma" (greenish color due to myeloperoxidase) - **Sites:** Skin, bone, soft tissues, CNS, mediastinum - **Frequency:** 2–10% of AML cases at diagnosis; 20–30% at relapse - **Prognosis:** Indicates aggressive disease and higher relapse risk **Clinical Pearl:** In this case, the patient has gum bleeding (gingival infiltration) and Auer rods (confirming AML). The most common *overall* site of extramedullary involvement is still the spleen/liver (hepatosplenomegaly), even though gingival involvement is prominent in monocytic subtypes. **Mnemonic: "SLANG"** — **S**pleen/**L**iver (most common), **A**cute monocytic (gingival), **N**ervous system (CNS), **G**ingival (monocytic AML). **Warning:** Do not confuse "most common site of extramedullary involvement" with "most common *type* of extramedullary involvement." Hepatosplenomegaly is the most common finding overall, but gingival infiltration is the most characteristic of monocytic AML.