Skill Checkup: An Elderly Man With Leg Pain and Weakness

Maria-Victoria Mateos, MD, PhD; Simon J. Harrison, MBBS, PhD


April 04, 2022

Because the MM at diagnosis was Bence Jones kappa, the current evaluation must now include serum and urinary assessments. Although the monoclonal protein is free light chain kappa eliminated by the urine, looking for serum-free light chains is a better test to perform given increased sensitivity and accuracy. Urinary collection over 24 hours is difficult for most patients. Detection of monoclonal proteins in the serum or urine is a strong clue to either a new diagnosis of MM or the occurrence of relapsed disease. Plasma cells, which may grow out of control and build up in the bone marrow, can release high levels of monoclonal protein, which lead to some of the complications associated with MM. The larger monoclonal proteins (also called monoclonal immunoglobulin, monoclonal spikes, or paraproteins; IgG, IgA, IgD, IgM) may be detected in serum. Light chains (kappa or lambda) are smaller fragments of immunoglobulin molecules that can be detected in serum (serum-free light chains) and are small enough to be filtered through the kidney (glomerulus) and can be detected in the urine (Bence Jones proteins).

An older person may have an elevated A1c and this can contribute to general weakness. However, this result will not provide as much definitive information as the presence of urinary monoclonal protein would provide. Likewise, although a blood culture may identify a specific pathogen, there are no specific signs of infection in this case.

Factors VIII and IX are clotting factors that are low in individuals with hemophilia (under 40% but usually only symptomatic below 5%, severe phenotype is less than 1%). Although patients with MM may report excessive bleeding associated with thrombocytopenia, clotting factors VIII and IX are not implicated. Rarely, amyloidosis (a related plasma cell disorder) can be associated with low factor X levels and excess bleeding owing to adsorption of factor X by the amyloid fibrils.


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