Background.Monoclonal gammopathy of undetermined significance (MGUS) is unusual in the general population aged <60 years. Various reports indicate a much higher incidence of monoclonal gammopathy among human immunodeficiency virus (HIV)–infected patients and a significantly younger age at diagnosis. We sought to describe the laboratory findings and clinical course of MGUS, including association with plasma cell disorders, other malignancies, and infections, in 25 HIV‐infected patients with a detectable serum monoclonal protein.

Methods.We reviewed the patients' demographic characteristics, stage of HIV infection, and clinical course. Laboratory studies included determination of CD4⁺ T lymphocyte cell counts, HIV type 1 loads, and quantitative immunoglobulin levels; serum and urine protein immunoelectrophoresis; and determination of serum viscosity indices. Skeletal surveys and bone marrow biopsies were performed in selected cases.

Results.Twenty‐four of 25 patients were male, and the median age of patients was 50 years (range, 21–69 years). The median CD4⁺ T lymphocyte count was 350 cells/μL (range, 40–1029 cells/μL; mean, 355 cells/μL), and the median HIV load was <75 copies/mL (range, <50 to 100,000 copies/mL; mean, 20,800 copies/mL). Thirteen of 25 patients had HIV viremia, despite receiving highly active antiretroviral therapy (HAART). After a mean follow‐up duration of 21 months, 7 patients (28%) received a diagnosis of a malignancy (multiple myeloma, in 1 patient; non‐Hodgkin lymphoma, in 1; Hodgkin lymphoma, in 1; Kaposi sarcoma, in 2; and plasmacytoma, in 2). Ten patients were coinfected with hepatitis B virus and/or hepatitis C virus; 6 were anemic. No patients developed renal failure or hypercalcemia. Nine (56%) of 19 evaluable patients had a decrease of serum monoclonal protein (mean, 0.5 g/dL) while receiving HAART.

Conclusions.Patients in our study were characterized by the detection of a monoclonal protein at a younger age and the increased presence of other viral infections (infection with hepatitis B or C virus or Kaposi sarcoma herpesvirus) than is typically seen in an HIV‐uninfected cohort. CD4⁺ T lymphocyte counts were relatively robust. HAART appeared to have a favorable impact on the serum monoclonal protein level in 9 patients. Long‐term follow‐up is needed to better define the natural history of MGUS and the link to other possible contributing factors.