This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
The following is the least useful investigation in multiple myeloma : 
Select and explain. 
A. ESR, B. X-Ray, C. Bone scan, D. Bone marrow biopsy
C: Bone scan
Answer: C: Bone scan 
Explanation: Answer is C (Bone scan) Bone scans are least useful for diagnosis of Multiple Myeloma. Cytokines secreted by myeloma cells suppress osteoblastic activity therefore typically no increased uptake is observed. In multiple myeloma the osteohlastic response to bone destruction is negligible. The bone scan therefore is often normal or may show areas of decreased uptake (photopenia).It has been found to be less useful in diagnosis than plain radiography. Ig protein /24 hour is a major ciriteria for diagnosis " align="left" height="133" width="100"> Note : Serum M component is most commonly IgG Q (IgG (53%), IgA (25%), IgD (I%) Bence Jones proteins are light chain protein only Q.