Authors’ Reply

We thank Kousios et al.¹ for their comments on monoclonal Ig–associated renal diseases in the setting of smoldering multiple myeloma (SMM). In their letter, they express concern that a diagnostic gap may be created if such patients are excluded from monoclonal gammopathy of renal significance (MGRS). We would like to clarify that the term MGRS does not exclude SMM. As we state in our paper, MGRS refers to renal disorders caused by a monoclonal Ig “in the absence of hematologic malignancy or other myeloma-defining events.”² Although the main premalignant plasma cell disorder responsible for most cases of MGRS is monoclonal gammopathy of undetermined significance in the setting of a small clonal proliferation, the term MGRS also includes similar renal injury that occurs in the setting of SMM, smoldering Waldenström macroglobulinemia, or monoclonal B cell lymphocytosis. It is possible that Kousios et al.¹ were concerned that, in figure 1 in our paper,² SMM appears under the category of “malignant” plasma cell disorders. We placed SMM in the “malignant” category to indicate the emerging concept that approximately 50% of patients with high-risk SMM are considered to have early malignancy and are being offered therapy with antimyeloma treatments in the absence of myeloma-defining events.³

The definition of MGRS will evolve over time, and it will even evolve in the individual patient. Thus, if the underlying plasma cell disorder in a patient with MGRS progresses to multiple myeloma, Waldenström macroglobulinemia, or malignant lymphoma, it will not be considered (or require a reason to be considered) as having MGRS. Similarly, as the strategy of using antimyeloma therapy for selected patients with SMM evolves, patients in whom therapy targeting the plasma cell clone is indicated will not be considered (or will require a reason to be considered) as having MGRS.

Disclosures

None.