Pleural effusion in a patient with multiple myeloma.

The results of a basic biochemical examination performed 2 weeks earlier were normal. Serum protein electrophoresis revealed hypoproteinemia (65 g/L; reference interval, 68– 73 g/L), associated with decreased γ globulins (4 g/L; reference interval, 9–15 g/L) but without a detectable paraprotein band. An assay for serum free light chain showed decreased κ light chains (0.5 mg/L; reference interval, 3.3–19.4 mg/L) and λ light chains (<0.3 mg/L; reference interval, 5.7–26.3 mg/L); the κ/λ ratio could not be accurately determined because of the low concentration of λ light chains. An examination of a bone marrow aspirate taken 3 months earlier showed dystrophic plasma cells accounting for 50% of the nucleated cells.