Amyloid cast nephropathy with systemic AL amyloidosis
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IMAGES IN HEMATOLOGY
Amyloid cast nephropathy with systemic AL amyloidosis Shinichi Mizuno1 · Hideyuki Kosukegawa1 Received: 23 September 2020 / Revised: 9 November 2020 / Accepted: 10 November 2020 © Japanese Society of Hematology 2020
Keywords Amyloidosis · Amyloid cast nephropathy · Bortezomib · Acute kidney injury (AKI) · Multiple myeloma A 68-year-old woman was admitted to our hospital with a high serum creatinine level of 3.4 mg/dL, anemia, and hypotension (77/44 mmHg). Serum and urinary immunoelectrophoresis detected Bence Jones-λ monoclonal protein. Bone marrow examination revealed 3–4% plasma cells, most of which were CD19-negative monoclonal plasma cells with dysplastic changes and λ-chain restriction. The level of serum κ-light chain was 41.8 mg/L and the λ-chain level was 4730 mg/L. Urinalysis showed proteinuria of 3.8 g/g creatinine, mostly non-albuminuric. Renal biopsy revealed tubulointerstitial nephritis with cast nephropathy. Direct fast scarlet staining was positive in the small arteries and the casts, but there was no evidence of glomerular deposits (Fig. 1a). Only λ-chain deposits in the casts were observed by light chain staining (Fig. 1b). Furthermore, amyloid deposits were found in the gastric mucosa and abdominal fat. The patient was diagnosed with systemic AL amyloidosis with acute kidney injury (AKI) caused by amyloid cast nephropathy. Three months after weekly bortezomib and dexamethasone therapy, her levels of serum creatinine and proteinuria markedly improved (1.5–1.7 mg/dL and 0.1–0.2 g/g creatinine, respectively). The λ-light chain level was also reduced by 98% and her blood pressure normalized. However, frailty caused by urinary tract infection and pneumonia made continuation of chemotherapy unfeasible after 3 years, and the patient died of multiple organ failure. On autopsy, there were few remaining amyloid casts. In general, cast nephropathy by myeloma is negative on amyloid staining, such as Congo red staining and direct fast scarlet staining, because it arises through formation
of casts without amyloid fibrillar structure by monoclonal light chain with a high affinity for Tamm-Horsfall protein. Renal involvement in AL amyloidosis typically presents as albuminuria-derived nephrotic syndrome, where the amyloid is predominately deposited in the glomeruli. In some cases complicated by renal dysfunction without proteinuria, amyloid deposits appear in tubules and small vessels. However, amyloid cast nephropathy with massive non-albuminuria and AKI is not well understood, and the pathogenesis of amyloid cast nephropathy remains unclear. One hypothesis is that amyloidogenic light chains are reabsorbed by proximal tubules, leading to amyloid formation and aggregation in the tubular cytoplasm, and subsequent excretion into the lumen. Therefore, casts composed of amyloidogenic light chains are considered to be positive for amyloid staining. In renal diseases caused by tubulointerstitial injury, including typical myeloma cast nephropathy, renal function improves if the pathogens are r
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