A 65-year-old man has anemia, splenomegaly, and extramedullary hematopoiesis. He has experienced easy fatigability, weightloss, and weakness. Bone marrow biopsy reveals marked proliferation of fibrous tissue (myelofibrosis) Which of the following is a characteristic finding in this disorder?

## **Core Concept**
The patient's presentation suggests a myeloproliferative neoplasm (MPN), specifically primary myelofibrosis (PMF), characterized by the progressive fibrosis of the bone marrow, leading to ineffective hematopoiesis and compensatory extramedullary hematopoiesis. This condition often presents with anemia, splenomegaly, and symptoms related to decreased blood cell production.

## **Why the Correct Answer is Right**
In primary myelofibrosis, a hallmark feature is the presence of **leukocyte-alkaline phosphatase (LAP) positivity**. LAP is an enzyme found in white blood cells, and its activity is often increased in PMF. This is in contrast to other myeloproliferative diseases like chronic myeloid leukemia (CML), where LAP activity is typically low. The increased LAP score is a helpful diagnostic clue, supporting the diagnosis of PMF over other causes of myelofibrosis or bone marrow failure.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option might suggest a low LAP score, which is more characteristic of CML, not PMF.
- **Option B:** While certain cytogenetic abnormalities are associated with PMF, this option does not directly relate to a characteristic finding like LAP positivity.
- **Option C:** This might imply a different diagnostic feature not specifically related to LAP or common diagnostic markers for PMF.
- **Option D:** This option could suggest another condition or test not directly related to the characteristic findings in PMF.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that **primary myelofibrosis often presents with a high LAP score**, which can help differentiate it from other myeloproliferative neoplasms like CML, where the LAP score is typically low. This distinction is crucial for diagnosis and management.

## **Correct Answer:** D. Increased leukocyte alkaline phosphatase (LAP) score.

✓ Correct Answer: B. Teardrop-shaped erythrocytes