Answer :USMLE step 2 Mcq 255:A 60yr old man presented with severe back pain after a long distance travel in a bus




Correct Answer: B

Multiple myeloma is a plasma cell cancer caused by the neoplastic proliferation of a single clone of immunoglobulin secreting cells. The neoplastic proliferation of a single clone of plasma cells results in the abnormal production of a single immunoglobulin (e.g. IgG as in the above problem) and associated paraproteins and light chains.These paraproteins and light chains accumulate in the kidneys and are secreted in the urine as protein casts (e.g.Bence Jones proteins etc.). The light chains and paraproteins also damage the kidney by accumulating in the convoluted tubules and collecting ducts. This results in elevated blood urea nitrogen and serum creatinine creating a picture resembling chronic renal failure.The proliferating plasma cells secrete several cytokines. These cytokines mediate the bone destruction which is responsible for the pathological fractures seen in multiple myeloma. Due to the bone destruction elevated levels of serum calcium and serum phosphate are seen.Vertebrae are the most common site of bone involvement and the destructive bone lesions are seen as sharply punched out lesions on an X-ray. So keeping in mind all these factors the diagnosis is multiple myeloma. Osteoporosis is not the correct answer because even though it presents as pathological bone fractures in old individuals it has no associated renal dysfunction. Also the serum electrophoresis does not show any abnormal immunoglobulins.Hyperparathyroidism also presents with pathological fractures and elevated serums calcium and phosphate level. But this is not the correct answer since hyperparathyroidism never shows protein casts in the urine. Also the serum electrophoresis for immunglobulins is normal.Chronic renal failure is a part of multiple myeloma which is the basic underlying disease. It is not the diagnosis for this patient.


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