Amyloid Proximal Tubulopathy and Amyloid Casts: An Unusual Finding in Multiple Myeloma.

Patients with multiple myeloma (MM) often develop renal manifestations. The majority of cases present as cast nephropathy, amyloid light-chain (AL) amyloidosis, and monoclonal immunoglobulin deposition disease. AL amyloidosis usually involves the glomeruli, blood vessels, and interstitium. It is extremely uncommon to find isolated intratubular deposition of AL amyloid. Our patient presented with rapid worsening of renal function due to isolated intratubular deposition of AL amyloid, where the biopsy revealed amyloid proximal tubulopathy and amyloid cast nephropathy. Our case provides new insights into the complicated pathophysiology of the abnormal light chains in MM. This case is, to our knowledge, the second case of amyloid proximal tubulopathy reported in literature.