How is monoclonal gammopathy of renal significance (MGRS) different from myeloma kidney?

The terminology around renal failure and myeloma is confusing and sometimes unnecessarily complicated.

Here is how I approach it:

1. Light chain (cast) nephropathy - This is from toxic injury to the nephron tubules from excess light chains. This is usually picked up on biopsy or can be ascertained from high light chain burden in the context of renal failure and evidence of large amounts of Bence Jones protein in the urine. This is directly attributable to myeloma, and therefore, I approach this situation as multiple myeloma that requires systemic therapy.
2. Light chain deposition disease or related conditions WITH other myeloma defining events: Treat as myeloma.
3. Light chain deposition or MGRS without myeloma defining events - MGRS is really a b...