Amyloid proximal tubulopathy: a novel form of light chain proximal tubulopathy

Features that characterize monoclonal light chain ("myeloma") cast nephropathy with immunofluorescence challenges and emphasis on electron microscopy

Renal disease is a common cause of morbidity and mortality in patients with plasma cell dyscrasias. The serum-free light chain assay is used in patients, mostly older, with unexplained acute kidney injury to screen for potential myeloma cast nephropathy. This study consists of a systematic review of diagnostic features in myeloma cast nephropathy. The morphological features of tubular casts in patients with multiple myeloma have not been systematically analyzed. This study focuses on the morphology of these casts, emphasizing ultrastructural features, in a series of 23 patients with light chain ("myeloma") cast nephropathy and compared them with casts in 10 patients with various diseases. The immunofluorescence data were correlated with morphological findings to provide diagnostic assessments and practice guidelines. The ultrastructural features identified as diagnostic of casts associated with myeloma included: amyloid and crystals in the casts, multiple well-defined fracture planes forming a complex jigsaw puzzle arrangement of cast contents, indicative of the fragility of the immunoglobulin light chains involved, and reactive tubular cells lining the tubules with the casts. These features were seen in 95.2% of MCN cases and none of the casts in other renal conditions. Myeloma casts exhibited light chain monoclonality in a significant percentage of the MCN cases and often no staining for IgA or IgM. In contrast, the majority of non-myeloma casts stained for both kappa and lambda light chains, lgA, and lgM, and showed ultrastructurally a rather uniform finely to coarsely granular electron density occasionally admixed with cellular debris.

Tubular basement membrane amyloid deposition: is it an indicator of renal progression in light chain amyloidosis?

In light chain amyloidosis (LA), the massive glomerular and vascular amyloid deposition leading to interstitial fibrosis/tubular atrophy (IFTA) is thought to be responsible for renal failure. The amyloid deposition in the interstitium and the tubular basement membrane (TBM) has received less attention in the study of LA. We, therefore, collected clinical and laboratory data on patients diagnosed with LA in our Nephrology Department and studied amyloid deposition in the TBM. Twelve LA patients were diagnosed by renal biopsy during a seven-year period. In 4 of the 12, amyloid deposition could also be detected in the TBM. In our first case of a patient with diabetes mellitus, non-amyloid fibrils resembling 'diabetic fibrillosis' were also seen by electron microscopy. Despite the double damage, IFTA was negligible, blood vessels were unaffected, and the glomerular deposition was segmental. In the other three cases, significant (>50%) IFTA and a severely reduced estimated glomerular filtration rate were already detected at the time of diagnosis and amyloid deposition was also observed in the blood vessels. These findings indicate the importance of TBM amyloid deposition in the progression of renal disease. This may represent a late-stage presentation of the disease with a heavy LC burden.

Non-crystalline light chain proximal tubulopathy, a morphologically protean entity

BACKGROUND

Light chain proximal tubulopathy (LCPT) is a rare form of paraprotein-related disease, occurring in two main histopathological forms: crystalline and non-crystalline. The clinicopathological features, treatment strategies and outcomes, especially of the non-crystalline form, are not well described.

METHODS

We conducted a single-centre retrospective case series of 12 LCPT patients, 5 crystalline and 7 non-crystalline, between 2005 and 2021.

RESULTS

The median age was 69.5 years (range 47-80). Ten patients presented with CKD and significant proteinuria (median estimated glomerular filtration rate of 43.5 ml/min/1.73 m2; urine protein:creatinine ratio 328 mg/mmol). Only six patients had known haematological disease at the time of renal biopsy. Multiple myeloma (MM) was diagnosed in seven patients cases and monoclonal gammopathy of renal significance (MGRS) in five patients. A clone was detected in all cases combining serum/urine electrophoresis and free light chain (LC) assays. Crystalline and non-crystalline variants had similar clinical presentations. For the non-crystalline variant, a diagnosis was reached based on a combination of CKD without another cause, haematological workup, LC restriction on immunofluorescence and abnormalities on electron microscopy (EM). Nine of 12 patients received clone-directed treatment. Patients who achieved haematological response (including all non-crystalline LCPT) had improved renal outcomes over a median follow-up of 79 months.

CONCLUSIONS

The non-crystalline variant may go unrecognised because of its subtle histopathological features and requires EM to distinguish it from 'excessive LC resorption without tubular injury'. Clone-directed treatment with good haematological response improves renal outcomes in both variants but limited data exist in MGRS. Multicentre prospective studies are needed to better define the clinicopathological characteristics associated with poor outcomes and optimize treatment strategies in patients with MGRS.

Coincidental light chain induced proximal tubulopathy with lupus nephritis: a case report and review of the literature

Background

We report a case of light chain proximal tubulopathy associated with lupus nephritis in a patient known to have systemic lupus erythematosus. The kidney can be injured in several ways in any of these disorders. Light chain proximal tubulopathy is a rare form of renal tubular injury that may occur in and complicate plasma cell dyscrasia, characterized by cytoplasmic inclusions of the monoclonal light chain within proximal tubular cells. Lupus nephritis is a common form of renal injury as it occurs in about 25–50% of adult patients with systemic lupus erythematosus.

Case presentation

We present a 57-year-old African patient known to have systemic lupus erythematosus and hypertension presented with a new complaint of microscopic hematuria. A renal biopsy was performed and revealed lupus nephritis class II concurrently associated with light chain induced proximal tubulopathy. A subsequent bone marrow biopsy was performed, which revealed multiple myeloma.

Conclusions

We report a case of coincidental lupus nephritis and proximal tubulopathy featuring a combined constellation of rare histopathological features that might add to the relationship between systemic lupus and paraproteinemia.

An autopsy case of amyloid tubulopathy exhibiting characteristic spheroid-type deposition

An 84-year-old woman with a history of haemodialysis for renal failure from approximately 1 year before death. Autopsy revealed numerous spheroid-type amyloid deposits in the kidney that were observed mainly in the interstitium but not the glomeruli and vessels. In addition, intracytoplasmic small globular amyloid deposits in the proximal tubules in addition to amyloid casts were identified. Immunohistochemistry and proteomic analyses indicated these deposits were composed of λ light chains. Amyloid deposition was also found in the lung and heart. λ-type monoclonal protein was detected in her serum and increased numbers of CD138-positive cells with λ-restriction was observed in the bone marrow. The case was diagnosed as amyloid tubulopathy (AT) associated with systemic ALλ amyloidosis related to plasma cell neoplasm. This case indicates that AT is associated with ALλ amyloidosis, which developed systemically with characteristic amyloid deposition forms. These pathological features may be associated with her rapid progressive renal failure.

Intratubular amyloid in light chain cast nephropathy is a risk factor for systemic light chain amyloidosis

Light chain cast nephropathy is the most common form of kidney disease in patients with multiple myeloma. Light chain casts may occasionally show amyloid staining properties, that is, green birefringence after Congo red staining. The frequency and clinical significance of this intratubular amyloid are poorly understood. Here, we retrospectively assessed the clinicopathological features of 60 patients with histologically proven light chain cast nephropathy with a specific emphasis on intratubular amyloid, especially, its association with extrarenal systemic light chain amyloidosis. We found intratubular amyloid in 17 cases (17/60, 28%) and it was more frequent in patients with λ light chain gammopathy (13/17 in the 'intratubular amyloid' group vs 19/43 in the 'no intratubular amyloid' group, P=0.02). Pathological examination of extrarenal specimens showed that intratubular amyloid was significantly associated with the occurrence of systemic light chain amyloidosis (5/13 in the 'intratubular amyloid' group vs 0/30 in the 'no intratubular amyloid' group, P=0.001). Our results indicate that first, intratubular amyloid is not a rare finding in kidney biopsies of patients with light chain cast nephropathy, and, second, it reflects an amyloidogenic capacity of light chains that can manifest as systemic light chain amyloidosis. Thus, intratubular amyloid should be systematically screened for in kidney biopsies from patients with light chain cast nephropathy and, if detected, should prompt a work-up for associated systemic light chain amyloidosis.

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.