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

What is the probable diagnosis in a patient with inc susceptibility to infection, Ig light chains in urine, and Rouleaux formation?

1. Cushing Syndrome

2. Polycythemia Vera

3. Carbon Monoxide Poisoning

4. Multiple Myeloma

The correct answer is: Multiple Myeloma

In this scenario, the patient's clinical presentation strongly suggests multiple myeloma as the probable diagnosis. The key indicators include increased susceptibility to infection, the presence of immunoglobulin light chains in the urine (often referred to as Bence Jones proteins), and rouleaux formation observed in the blood. Multiple myeloma is a hematologic malignancy characterized by the proliferation of monoclonal plasma cells in the bone marrow, leading to overproduction of immunoglobulins. This overproduction can result in the presence of free light chains in the urine, indicative of the disease, as these light chains are not adequately paired with heavy chains to form functional antibodies. The light chain cast nephropathy also contributes to renal impairment, further exacerbating the patient's susceptibility to infections. Rouleaux formation occurs due to the increased levels of proteins in the serum, particularly monoclonal immunoglobulins that can lead to a higher viscosity of blood. In multiple myeloma, the abnormal proteins cause the red blood cells to adhere to one another, which is visible as rouleaux on a blood smear. The combination of these findings—the immunoglobulin light chains in the urine, increased frequency of infections due to immunosuppression caused by the disease, and the presence