In which condition is roulaeux formation typically observed under microscopy?

• A. Polycythemia vera
• B. Multiple myeloma
• C. Aplastic anemia
• D. Thrombocytosis

Answer: (B)

Rouleaux formation is characterized by the stacking of red blood cells, resembling a pile of coins, which occurs due to increased plasma protein levels that facilitate intercellular adhesion. This phenomenon is typically observed in multiple myeloma, a hematological malignancy associated with the proliferation of monoclonal plasma cells. In multiple myeloma, the excessive production of immunoglobulins leads to elevated levels of proteins in the plasma, creating an environment where red blood cells are more prone to aggregate.

Rouleaux formation is less commonly seen in other conditions such as polycythemia vera, where increased red blood cell mass can lead to increased viscosity but does not primarily cause rouleaux formation due to protein content. Aplastic anemia involves a decrease in blood cell production and is characterized by a lack of red cells rather than their abnormal stacking. Thrombocytosis, an increase in platelet count, does not directly influence red blood cell morphology to cause rouleaux formation.

Thus, the presence of rouleaux formation primarily indicates increased plasma proteins, making multiple myeloma the most appropriate condition associated with this microscopic finding.