What laboratory finding typically differentiates multiple myeloma from Waldenström's macroglobulinemia?

Multiple myeloma and Waldenström's macroglobulinemia are both plasma cell disorders but exhibit distinct laboratory findings that help in their differentiation. The presence of osteolytic lesions is particularly characteristic of multiple myeloma. These lesions occur due to the activity of osteoclasts stimulated by the excessive production of osteoclast-activating factors by myeloma cells, leading to bone destruction and pain.

In contrast, Waldenström's macroglobulinemia, which is defined by the overproduction of IgM by lymphoplasmacytic cells, does not typically present with osteolytic lesions. Instead, this condition is more associated with symptoms arising from hyperviscosity due to the increased levels of IgM in the blood.

While both conditions can present with monoclonal gammopathy and may result in the presence of Bence-Jones proteins in urine (in cases of free light chain production), these findings are not exclusive or definitive for differentiating between the two. Hyperviscosity is a symptom seen in Waldenström's and not in multiple myeloma, but it does not provide the same clear distinction as the presence of osteolytic lesions does. Therefore, the identification of osteolytic lesions is