Case Presentation: A 66 year-old man presented with six months of migratory body aches, slowed walking and twenty-pound weight loss. He had no neurological deficits. Labs showed hemoglobin 10.5 g/dL, creatinine 1.2 mg/dL, and normal erythrocyte sedimentation rate, creatine kinase, thyroid stimulating hormone, prostate-specific antigen and liver tests. Serum protein electrophoresis (SPEP) showed hypogammoglobulinemia with no monoclonal protein (M protein). He was admitted 1.5 months later for intractable back pain and found to have creatinine 3.9 mg/dL, random urine protein-to-creatinine ratio 9.4 and calcium 11.9 mg/dL. There was a soft tissue mass in the L2 vertebral body with epidural extension on MRI. CT scan obtained prior to IR-guided fine needle aspiration of this mass revealed multiple other lytic lesions in the spine. Free kappa/lambda ratio was 0.05 and immunofixation showed free lambda. Repeat SPEP showed M protein in the beta region, as did urine protein electrophoresis (UPEP). Atypical plasma cells staining positive for lambda had replaced 90% of the bone marrow on biopsy.
Discussion: Our patient presented with vague but concerning symptoms that raised suspicion for a variety of etiologies. His initial SPEP was deceptive. Even when he developed acute renal failure, heavy proteinuria and was found to have an infiltrative bone mass, a clonal plasma cell disorder was not foremost on the differential because of the lack of M protein on the SPEP. Instead, efforts focused on the biopsy of the spinal mass when less invasive testing could have elucidated the diagnosis of light chain myeloma earlier.
Light chain myeloma comprise up to 20% of all forms of multiple myeloma. Multiple myeloma is the expansion of a clone of plasma cells which infiltrates the bone, suppresses the production of normal blood cells and stimulates osteoclastic activity. These neoplastic cells almost always produce monoclonal protein, which usually appears as a spike in the gamma region of the SPEP. However, the sole expression of light chains (and lack of heavy chains) in light chain myeloma may manifest as a decrease in the size of the gamma region (hypogammoglobulinemia). Because of rapid excretion in the urine, serum concentrations of monoclonal light chains may be initially too low to register as a spike on SPEP. Renal failure, which is more common in light chain myeloma than in other forms of multiple myeloma, cause serum concentrations of M proteins to rise, in this case to a detectable level on SPEP. Tests more sensitive than SPEP are needed to detect light chain myeloma earlier in its course. Immunofixation in addition to SPEP increases the sensitivity of detecting a monoclonal peak from 82% to 93% in patients with myeloma. Adding a free light chain assay or UPEP increases the sensitivity to 97%.
Conclusions: When there is high clinical suspicion for multiple myeloma, SPEP must be sent in conjunction with more sensitive tests to detect variants such as light chain myeloma. Because renal failure is more common in light chain myeloma, early detection is key. Diagnosing light chain myeloma requires looking beyond the SPEP.
To cite this abstract:Liu M, Arad D. Looking Beyond the Lone Peak. Abstract published at Hospital Medicine 2015, March 29-April 1, National Harbor, Md. Abstract 595. Journal of Hospital Medicine. 2015; 10 (suppl 2). https://www.shmabstracts.com/abstract/looking-beyond-the-lone-peak/. Accessed July 21, 2019.