16 February 2007 – Case of the Week #74
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We thank Dr. Tina Dadu, Sir Ganga Ram Hospital, New Delhi, India, for contributing this case. We invite you to contribute a Case of the Week by sending an email to NPernick@PathologyOutlines.com with microscopic images (any size, we will shrink if necessary) in JPG or GIF format, a clinical history, your diagnosis and any other images (gross, immunostains, EM, etc.) that may be helpful or interesting. We will write the discussion (unless you want to), list you as the contributor, and send you a check for $35 (US) for your time after we send out the case. Please only send cases with a definitive diagnosis.
Case of the Week #74
Clinical history
A 65 year old woman presented with backache and paraparesis. A bone marrow biopsy and lab tests were obtained.
Bone marrow images: #1; #2; #3; #4; #5; #6
Lab tests: serum protein electrophoresis; urine immunofixation electrophoresis
What is your diagnosis?
(scroll down to continue)
Diagnosis:
Multiple myeloma, light chain (kappa) subtype
Discussion
The bone marrow smears show anaplastic plasma cells and lymphoplasmacytoid lymphocytes. The serum protein electrophoresis does not show a monoclonal band, as would be expected in classic myeloma. The urine immunofixation electrophoresis shows a prominent monoclonal band in the kappa region, but no heavy chaín immunoglobulins. These features are diagnostic of the light chain subtype of myeloma.
In light chain myeloma (also called Bence Jones myeloma), the neoplastic cells produce free monoclonal light chains but no associated heavy chain or complete immunoglobulin. They represent 15-20% of all myeloma cases, and apparently are caused by the absence of IgH rearrangement at the DNA level, reflecting possible abnormalities in IgH gene recombination during B-cell maturation (Blood 2004;103:3869). The monoclonal light chains are small enough to be freely filtered by the kidneys, and become Bence-Jones proteins.
These patients may be diagnostic problems. Their serum electrophoresis is normal and serum total protein is normal or low, which is not typical for myeloma. They also have low serum gamma globulins, in contrast to the elevated levels in classic myeloma. The traditional key to diagnosis is examination of urine, which contains Bence-Jones proteins. Urine electrophoresis shows a monoclonal spike, and immunofixation locates it in the kappa or lambda region. If one suspects light chain disease, there is now a serum antibody assay (Freelite) that is diagnostic (Lancet 2003;361:489, corporate link).
Due to the heavy production of light chains, these patients often also have light chain deposition disease in the kidney (click here for this topic in the Kidney non-tumor chapter of PathologyOutlines.com).
Surprisingly, despite the high prevalence of this disease, there appear to be no recent reviews of light chain myeloma discussing its prognosis or treatment.
Nat Pernick, M.D., President
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