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A woman in her 70s presented with numbness in her hands that had progressively worsened over the last 6 months.. She did not have diabetes mellitus and she did not drink alcohol. On physical examination, she had no pallor, lymphadenopathy, or organomegaly. She had evidence of bilateral carpal tunnel syndrome (positive Phalen test and Tinel sign bilaterally) and reduced deep tendon reflexes in the upper and lower extremities bilaterally. Laboratory test results for complete blood cell count, serum calcium, serum creatinine, blood glucose, serum thyroid-stimulating hormone, and serum B12 were within normal limits. Because of unexplained neuropathy, a workup to detect an underlying monoclonal gammopathy was done, including serum protein electrophoresis, immunofixation, and free light chain assay (see Table).
Rajkumar SV, Kyle RA. Protein Electrophoresis and Immunofixation for the Diagnosis of Monoclonal Gammopathies. JAMA. 2014;312(20):2160-2161. doi:10.1001/jama.2014.8237