Background/Purpose: Monoclonal gammopathy of undetermined significance (MGUS) has been associated with osteoporosis, neuropathy, pernicious anemia, and low vitamin B12, and may precede multiple myeloma and lymphoplasmacytic disorders.  The purpose of this study is to determine the characteristics of a group of MGUS patients diagnosed in an outpatient rheumatology disease unit.

Methods: A retrospective chart review was conducted of patients found to have MGUS, including history and physical, laboratory and x-ray studies.  Patients were excluded if they had a preexisting lymphoproliferative disorder, if myeloma was subsequently diagnosed, or a repeat immunofixation did not show a paraprotein.

Results: There were 39 males and 71 females, ranging in age from 31 to 101 (mean 77 years).  The reasons for referral included subacute fracture of spine or pelvis-59, osteoporosis evaluation-11, inflammatory arthritis-16, degenerative and crystal induced arthritis-20, neuropathy-1, and abnormal laboratory result-3. Preexisting conditions included:  history of solid tumor-29, previous major osteoporotic fracture-63, hepatitis C-4,, RA-7, SLE-3, Sjogren’s-2, ulcerative colitis-3, thyroid disease-17, myasthenia gravis-1, and primary biliary cirrhosis-1. Neuropathy defined by a sensory loss above the ankle was found in 66 patients.  Paraprotein was identified by serum immunofixation in 93 patients:  IgG 68 %, IgM 18%, IgA-14% with 56 % lambda and 44% kappa chains.  Serum protein electrophoresis failed to show M-spike in 20 of these patients.  Light chains only were found among the remaining 17 patients; 3 kappa and 14 lambda.  Urine immunofixation was positive in 32 out of 77 tested.  Among the neuropathy patients,14 had IgM, 37 IgG, 4 IgA paraprotein, 8 lambda only and 3 kappa only light chains.  Pernicious anemia was diagnosed in 15 patients based on low vitamin B12 levels and the presence of either intrinsic factor or anti-parietal cell antibody.  79 of the 110 patients had either osteoporotic fracture, neuropathy, or PA.  Upon follow up one lupus patient was subsequently diagnosed with plasmablastic lymphoma and the one patient referred for neuropathy was diagnosed with follicular lymphoma

Conclusion: Rheumatologists will most likely encounter MGUS among patients evaluated for osteoporosis.  Neuropathy, pernicious anemia, and previous fracture should prompt investigation with immunofixation as a screening test.  If a MGUS is found and work up for myeloma is negative, studies for lymphoproliferative disorder should be considered in at risk patients.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/110-patients-with-monoclonal-gammopathy-of-undetermined-significance-mgus-in-a-rheumatology-disease-unit-fracture-neuropathy-and-pernicious-anemia-are-clues-to-recognition/