Final answer:
In multiple myeloma, an increased level of abnormal antibodies or paraproteins leads to a decreased anion gap by contributing positively charged proteins into the blood and causing renal impairment.
Step-by-step explanation:
The anion gap can decrease in multiple myeloma predominantly due to the accumulation of paraproteins like Bence Jones proteins. These proteins are positively charged and can reduce the measured concentration of other anions in the serum, leading to a lower anion gap. Additionally, multiple myeloma patients may experience renal impairment, which can also contribute to a reduction in the anion gap by affecting the ion balance.
Multiple myeloma can lead to the production of abnormal antibodies or paraproteins, such as monoclonal proteins (M proteins), which can be identified through immunoelectrophoresis (IEP). IEP reveals a distinct band in the gamma globulin region, indicating the production of a monoclonal protein rather than the normal broad smear of proteins. Such findings suggest a pathology like multiple myeloma, where excessive immunoglobulin light chains can circulate in the blood and get excreted in urine as Bence Jones protein.
The decrease in the anion gap due to multiple myeloma is an indirect result of abnormal protein production and renal impairment, which are central to the pathology of the disease.