USMLE (United States Medical Licensing Examination) Step 1 Practice Exam

What is the most likely diagnosis in a patient with Rouleaux formation in blood smear, M spike on serum protein electrophoresis, and increased osteoclast activity?

1. Polycythemia Vera

2. Multiple Myeloma

3. Corticosteroid-induced eosinopenia

4. Chronic Kidney Disease

The correct answer is: Multiple Myeloma

The presence of rouleaux formation in a blood smear suggests an increased protein concentration in the serum, which is often associated with conditions that produce excess proteins, such as multiple myeloma. In this condition, there is an overproduction of monoclonal immunoglobulins, leading to the characteristic M spike observed on serum protein electrophoresis. This spike reflects the presence of a single clone of plasma cells that are producing a large amount of a specific antibody. Increased osteoclast activity is another important finding associated with multiple myeloma. This is due to the activation of osteoclasts by factors secreted by myeloma cells, resulting in bone resorption and pathological fractures, often leading to skeletal-related events in patients. The combination of these findings—rouleaux formation, the M spike on serum protein electrophoresis, and increased osteoclast activity—strongly points to multiple myeloma as the most likely diagnosis. In contrast, conditions like polycythemia vera, corticosteroid-induced eosinopenia, and chronic kidney disease do not share this specific triad of clinical and laboratory findings, making them less likely in this scenario.