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Immunoglobulin light chain amyloidosis is the most frequent type of renal amyloidosis in the United States, accounting for 81% of cases. Accurate typing is crucial for early diagnosis and treatment of immunoglobulin-derived amyloidosis and to avoid treating other amyloidoses with potentially toxic chemotherapy. Immunofluorescence is the first step to type renal immunoglobulin-derived amyloidosis but the performance characteristics of this method are largely unknown. Here, we establish the sensitivity and specificity of immunofluorescence for diagnosing immunoglobulin-derived amyloidosis in patients whose amyloid typing was performed by the current gold standard of laser microdissection/mass spectrometry. Renal biopsy pathology reports originating from several institutions with a diagnosis of amyloidosis and which had amyloid typing by laser microdissection/mass spectrometry performed at our center were reviewed. Reported immunofluorescence staining for kappa or lambda of 2+ or more, with weak or no staining for the other light chain was considered positive for light chain amyloidosis by immunofluorescence. Based on microdissection/mass spectrometry results, of the 170 cases reviewed, 104 cases were typed as immunoglobulin-derived amyloidosis and 66 were typed as non-immunoglobulin-derived amyloidosis. Immunofluorescence sensitivity for diagnosing immunoglobulin-derived amyloidosis was 84.6%. The remaining 16 cases could not be diagnosed by immunofluorescence due to reported weak staining for all antigens or reported lack of preferential staining for one antigen. Immunofluorescence specificity was 92.4%. Five cases, all amyloid A amyloidosis, were misdiagnosed as immunoglobulin-derived amyloidosis by immunofluorescence. Immunofluorescence failed to accurately differentiate immunoglobulin-derived from non-immunoglobulin-derived amyloidosis in 12.3% of cases of renal amyloidosis. Relying on immunofluorescence alone for determining immunoglobulin-derived vs. non-immunoglobulin-derived amyloidosis may lead to misdiagnosis. Thus, immunofluorescence has inferior sensitivity and specificity compared with laser microdissection/mass spectrometry in the typing of immunoglobulin-derived amyloidosis.

Novel anticancer therapies are changing the landscape of clinical oncology and nephrology practice. With improved survival rates, many cancer survivors are developing kidney disease as a result of their cancer treatment. As a consequence, a new medical sub-specialty has emerged, termed “onco-nephrology.” Onco-nephrology is a broad term encompassing acute and chronic kidney disease from cancer therapy as well as other effects, such as hypertension and electrolyte disturbances. For the practicing nephrologist, it is important to be aware of emerging toxicities from relatively newer anticancer therapies. In this review, we provide an update on the renal toxicity of emerging anticancer therapies, including immune checkpoint inhibitors, angiogenesis inhibitors, and BRAF inhibitors.

Monoclonal immunoglobulin light chain (LC) crystalline inclusions within podocytes are rare, poorly characterized entities. To provide more insight, we now present the first clinicopathologic series of LC crystalline podocytopathy (LCCP) encompassing 25 patients (68% male, median age 56 years). Most (80%) patients presented with proteinuria and chronic kidney disease, with nephrotic syndrome in 28%. Crystalline keratopathy and Fanconi syndrome were present in 22% and 10%, respectively. The hematologic condition was monoclonal gammopathy of renal significance (MGRS) in 55% and multiple myeloma in 45%. The serum monoclonal immunoglobulin was IgG κappa in 86%. Histologically, 60% exhibited focal segmental glomerulosclerosis (FSGS), often collapsing. Ultrastructurally, podocyte LC crystals were numerous with variable effacement of foot processes. Crystals were also present in proximal tubular cells as light chain proximal tubulopathy (LCPT) in 80% and in interstitial histiocytes in 36%. Significantly, frozen-section immunofluorescence failed to reveal the LC composition of crystals in 88%, requiring paraffin-immunofluorescence or immunohistochemistry, with identification of kappa LC in 87%. The LC variable gene segment, determined by mass spectrometry of glomeruli or bone marrow plasma cell sequencing, was IGKV1-33 in four and IGKV3-20 in one. Among 21 patients who received anti-plasma cell-directed chemotherapy, 50% achieved a kidney response, which depended on a deep hematologic response. After a median follow-up of 36 months, 26% progressed to kidney failure and 17% died. The mean kidney failure-free survival was 57.6 months and was worse in those with FSGS. In sum, LCCP is rare, mostly associates with IgG κappa MGRS, and frequently has concurrent LCPT, although Fanconi syndrome is uncommon. Thus, paraffin-immunofluorescence and electron microscopy are essential to prevent misdiagnosis as primary FSGS since kidney survival depends on early diagnosis and subsequent clone-directed therapy.