Cast nephropathy (myeloma kidney) is the most common effect on the kidneys by multiple myeloma. Free light chains are freely filtered over the filtration barrier. In high concentrations, the free light chains will precipitate as casts in the tubules. This initiates immune reactions and acute kidney failure occurs. In the histopathological examination, casts can be found in the tubules (picture from Helge). The treatment consists of treating the underlying disease to reduce the production of light chains. Special filtres with large pores have been tested in patients who require dialysis to remove the light chains from circulation, but the treatment is still under experimentation.
Severe hypercalcemia can occur in multiple myeloma due to skeleton breakdown. Hypercalcemia works diuretically and the patient can become quite dehydrated with prerenal kidney failure, and eventually develop acute tubular necrosis as a result. Rehydration is the most important treatment in addition to reducing the serum calcium levels by giving the patient bisphosphonates and thereby building calcium back into the skeleton.
AL amyloidosis can also affect the kidneys and lead to proteinuria that can result in nephrotic syndrome. The treatment is based on treating the underlying disease.
Other effects on glomeruli or tubules by multiple myeloma can appear and be found in the kidney biopsy. A biopsy of myelomatosis patients with affected kidneys is therefore desired for the final diagnosis.