Acute kidney injury due to tubular intraluminal monoclonal light chain crystals mimicking acute pyelonephritis

Abstract

Tubular intraluminal inflammatory cells may be seen in kidney biopsies of patients with pyelonephritis, cell-mediated transplant rejection, autoimmune tubulointerstitial nephritis, allergic reactions, or in association with monoclonal light chain casts. When casts in a native kidney are primarily composed of granulocytes, the cause is most commonly acute pyelonephritis due to an ascending bacterial urinary tract infection. We report a 57-year-old man with acute kidney injury and an intense intraluminal neutrophil response to monoclonal lambda light chain crystal containing casts.

• Acute kidney injury
• light chain cast nephropathy
• multiple myeloma

Background

Multiple myeloma and other lymphoproliferative disorders often cause kidney disease. The spectrum of associated kidney pathology includes myeloma kidney (cast nephropathy), amyloidosis, light chain proximal tubulopathy (LCPT), monoclonal immunoglobulin deposition disease, and rarely monoclonal light chain deposits along the tubular basement membranes. Tubular intraluminal inflammatory cells may be seen in kidney biopsies of patients with monoclonal light chain casts, but may also be seen in pyelonephritis, cell-mediated transplant rejection, autoimmune tubulointerstitial nephritis, or allergic reactions.¹ When the primary composition of the inflammatory component are granulocytes, acute pyelonephritis is the most common finding.² We present an interesting biopsy finding in a patient with multiple myeloma who presented with acute kidney failure. The histology revealed an intense neutrophilic inflammatory response associated with crystallization of light chains of lambda (λ) type in the lumen of tubules.

Case report

Clinical history and initial laboratory data

A 57-year-old African-American man presented to the hospital with weakness and fatigue of 2 weeks duration. He had not sought medical care for many years and was not currently taking any medications. On admission, the serum creatinine level was 7.4 mg/dL. On examination, the patient appeared ill with a weight of 193 pounds and a body mass index of 26.2 kg/m². His heart rate was 70 beats/min and regular and blood pressure was 130/80 mmHg. Examination of chest and abdomen were unremarkable. Extremities showed no edema. Laboratory findings at presentation are listed in Table 1, notable for urinalysis with dipstick trace positive for albumin. The spot urine protein/creatinine ratio was 1.2. He had a leukocytosis with neutrophilia (86% neutrophils) but no immature band forms seen. Anemia was also discovered on presentation. The kidneys were markedly enlarged by renal ultrasonogram, with long axis dimensions measuring 16.3 cm for the right kidney and 15 cm for the left kidney. Renal cortical echogenicity was normal, and there was no evidence of a mass, stone or hydronephrosis. A kidney biopsy was arranged before results of serologic testing were available to determine the etiology of kidney injury.

Table 1. Laboratory results.

	On admission (normal value)
Sodium (mEq/L)	127 (133–145 mEq/L)
Potassium (mEq/L)	4.2 (3.5–4.8 mEq/L)
Blood glucose (mg/dL)	136 (70–90 mg/dL)
Serum calcium (mg/dL)	9.1 (8.4–10.2 mg/dL)
Blood urea nitrogen (mg/dL)	85 (6–20 mg/dL)
Serum creatinine (mg/dL)	7.4 (0.7–1.2 mg/dL)
Serum albumin (g/dL)	2.8 (3.5–5.2 g/dL)
Serum total protein (g/dL)	7.8 (6–8.3 g/dL)
Erythrocyte sedimentation rate (mm/h)	138 (0–10 mm/h)
Hemoglobin (g/dL)	9.2 (14–18 g/dL)
Hematocrit (%)	27.3 (42%–52%)
Mean corpuscular volume (fl)	101.4 (80–99 fl)
White blood cell count (10^3/L)	15.8 (4–11 × 10^3/L)
Platelet count (10^3/L)	201 (150–450 × 10^3/L)
Estimated GFR (mL/min; 4-point  Modification of Diet and  Renal Disease Study equation)	9
Urinalysis	Trace protein, 2 RBCs, 56 WBCs, no casts
Protein/creatinine ratio	1.2

Notes: Conversion factors for units: serum sodium and potassium levels expressed in mEq/L and mmol/L are equivalent; blood urea nitrogen in mg/dL to mmol/L, x0.357; GFR in mL/min to mL/s, x0.01667; creatinine in mg/dL to mmol/L, x88.4; albumin, protein, and hemoglobin in g/dL to g/L, x10; total bilirubin in mg/dL to µmol/L, x17.1; platelets and white blood cell count in x 10³/µL and x10³/L are equivalent; glucose in mg/dL to mmol/L, x 0.0551; calcium in mg/dL to mmol/L, x 0.2495; Abbreviation: GFR, glomerular filtration rate.

Kidney biopsy

Tissue submitted for light microscopy contained four (4) cores of renal cortex containing sixty-two (62) glomeruli, seven (7) of which were globally sclerosed. The remaining glomeruli were relatively unremarkable without cellular proliferation, capillary wall changes or expansion of mesangium. The distal tubules showed marked, diffuse white blood cell casts composed of mainly neutrophils, which were also infiltrating the tubular epithelium (Figure 1). There were strongly eosinophilic, sharply demarcated crystalline (mostly rhomboid, rectangular, and needle shaped) structures of varied geometric shapes within tubular lumina admixed focally with the neutrophil casts (Figure 1). The tubular lumina contained exclusively crystalline structures without fragmented amorphous proteinaceous casts, having a variegated staining pattern. These crystal containing casts differ from Bence–Jones cast nephropathy as well as other forms of tubulointerstitial injury seen in the setting of plasma cell dyscrasia (Table 2). Several tubules were ruptured with a surrounding non-caseating granulomatous reaction. There was marked interstitial edema as well as diffuse acute inflammation composed of neutrophils and eosinophils. The proximal tubules were spared though they appeared relatively simplified. The arterial vessels did not show significant sclerosis or display an accumulation of hyaline or amorphous pale-staining material. A Congo red stain was negative in the glomeruli, tubulointerstitium, and vessels.

Figure 1. (A) Tubules showing extensive neutrophil inflammation with eosinophilic crystals (A. 20× [inset 60×], H&E). (B) Granulomatous response to tubular rupture (20×, H&E). (C) Rhomboid and needle shaped intraluminal crystals (40×, H&E). (D) Ultrastructurally, there were needle shaped and rhomboid intraluminal hyperdense crystalline structures (×4000).

Table 2. Tubulointerstitial diseases associated with plasma cell dyscrasias.

	Tubular intraluminal cast/Crystal accumulation
	Shape	Color/Staining	Associated Cells/Material	Composition/Immuno-fluorescence findings	Tubulointerstitial involvement
Light Chain Crystal Casts	Crystalline, sharp edges, varied shapes	Homogeneous, strongly eosinophilic on H&E, pale PAS positive, congo red negative	May have neutrophil rich response	Kappa or Lambda light chain strongly predominant	Reactive inflammatory response, mononuclear or neutrophils
Bence–Jones Cast Nephropathy^a	Amorphous, fragmented, sharp and sometimes angulated borders	Variegated, brightly eosinophilic on H&E, pale on PAS, red on trichrome, congo red negative	Complexed with Tamm–Horsfall protein (uromodulin) and mononuclear cells +/− giant cells, sloughed tubular cells	Acutely, mainly kappa or lambda light chains. If subacute or chronic, mixed light chain pattern. Uromodulin positive by IHC.	Reactive inflammatory response in the interstitium
Monoclonal Immunoglobulin Deposition Disease^a	No intraluminal cast formation	N/A	No associated intraluminal cells	Monoclonal light and/or heavy chain strongly predominant along the TBM and within glomeruli	Reactive interstitial inflammation. Irregular thickening of the tubular basement membranes. PAS positive, congo red negative
Amyloid^a	May rarely have intraluminal amyloid casts	Amorphous, congo red positive	No associated intraluminal cells.	Monoclonal light chain strongly predominant along TBM, interstitium, and glomeruli in same areas as congo red. Fibrillary deposits by EM	Amorphous material deposition along the TBM and/or within the interstitium
Light Chain Tubulopathy	No intraluminal cast formation	N/A	Rare inflammatory cells. May find crystals within tubular epithelial cells.	Excess light chains within lysosomes of proximal tubules	Acute tubular injury only by light microscopy. Increased vacuoles +/− crystalline inclusions by EM
Tubulointerstitial nephritis with tubular basement membrane deposits	No intraluminal cast formation	N/A	No associated intraluminal cells	Scant monoclonal deposits along TBMs, may only be found using immunoelectron microscopy	Interstitial inflammation with mononuclear cells

Notes: Monoclonal immunoglobulin deposition disease and amyloid may also show glomerular involvement.

^aThese entities may overlap in the same patient. Abbreviations: IHC – immunohistochemistry, TBM – tubular basement membrane.

Immunofluorescence (IF) microscopy (renal cortex with 14 glomeruli) revealed no glomerular staining for IgG, IgA, lgM, C3, C1q, kappa, or lambda light chains. The tubulointerstitial compartment was also negative for all antibodies, but no casts were identified in the frozen tissue by DiffQuik analysis. Special stains for bacteria (Gram stain), fungus (GMS), and acid fast bacilli (AFB) were all negative. Immunoperoxidase staining on the formalin-fixed paraffin embedded tissue for kappa and lambda light chains showed strong lambda positivity (3+) within the well-defined, intra-tubular crystals and no significant kappa staining (Figure 2).

Figure 2. A&B: The crystals stained intensely (3+) for lambda light chains (A) but not (0) for kappa light chains (B), Immunoperoxidase stains, 40×.

Electron microscopy showed several tubular segments containing rectangular or rhomboid-shaped, osmiophilic crystals in the lumina with well defined, sharp edges, surrounded by predominantly neutrophils and admixed with the crystalline deposits (Figure 1D). The tubular epithelial cells demonstrated marked injury but no intraepithelial crystals were present in a large sample examined. On EM of the glomerulus, the capillary basement membranes display a smooth and regular contour and a mean thickness of 400 nm. The foot processes were preserved and the visceral epithelial cells were unremarkable. No immune complex-type electron dense deposits, fibrillar, or crystalline deposits were seen along the capillary basement membranes, in glomerular cells or within the mesangium.

Diagnosis

Bence–Jones (monoclonal lambda light chain) crystal containing cast nephropathy with a predominant granulocytic response.

Clinical follow-up

Following the biopsy results, the patient was found to have a monoclonal IgG-lambda protein measuring 2.8 g/dL by serum protein electrophoresis and immunofixation studies along with elevated serum free lambda light chains (5140 mg/L) and markedly decreased free kappa/Lambda ratio (0.01). A bone marrow biopsy showed 19% monoclonal plasma cell of λ-type. A bone survey showed superficial intracortical osteolytic lesion in the anterior aspect of the right femoral shaft. The patient had fever of unknown origin, which delayed chemotherapy initiation for 2 weeks. Blood and urine cultures were repeatedly negative despite being on no antibiotic therapy for the first few days of admission and prior to the biopsy. Infectious disease specialists evaluated the patient and concluded the fever and elevated ESR were due to the underlying malignancy. His initial low albumin was ascribed to poor PO intake, inflammation, and potential chronic liver disease.

Treatment for symptomatic multiple myeloma was started with Bortezomib, receiving four courses (1.3 mg/m²/day, four infusions at Days 1, 4, 8, and 11) with dexamethasone. The kidney failure resolved after three cycles of therapy, and patient no longer required hemodialysis after four weeks of chemotherapy. After treatment, the eGFR and creatinine were >60 mL/min and 1.0 g/dL respectively, 30 days following start of chemotherapy. Hemoglobin increased to 12.4 g/dL and the WBC count decreased to 9.9 × 10³/L. The serum-free lambda light chain decreased to 70.11 mg/L (Kappa/Lambda ratio 0.12 L). Currently, the patient is being evaluated for an autologous stem cell transplant.

Discussion

Renal injury in a patient with monoclonal light chains is most commonly due to Bence–Jones cast nephropathy (myeloma kidney), monoclonal immunoglobulin deposition disease (MIDD), amyloidosis, or light chain proximal tubulopathy (LCPT).3 In LCPT the excessive light chains (LCs), mostly kappa type, are excreted through the kidney and are reabsorbed in the proximal tubular cells with or without crystal formation in the cytoplasm, leading to tubular damage. This often results in acquired Fanconi syndrome characterized by aminoaciduria, glycosuria, phosphaturia, bicarbonate, and uric acid wasting.4 When MIDD and AL amyloidosis affect the tubulointerstitial compartment, they tend to deposit along the tubular basement membranes leading to irregular thickening either with PAS positive material which stains for the monoclonal light chain and leads to acute renal failure (MIDD) or an amorphous waxy accumulation of PAS negative, Congo Red positive material frequently in a globular pattern (amyloid).3 Rarely amyloid casts may also precipitate within the tubular lumen, also congo red positive.5 Cast nephropathy shows precipitation of sharply-demarcated, brittle casts admixed with uromodulin in the distal tubules with a distinct morphologic and staining pattern. Monoclonal light chains may also deposit within the tubular basement membranes and cause non-specific tubulointerstitial nephritis, wherein the deposits may only be localized using immunoelectron microscopic methods, called immunogold labeling.6

This case is unique in that the intraluminal casts are more crystalline in appearance and elicit a striking neutrophil-rich response which mimics acute pyelonephritis. Acute pyelonephritis was excluded by serially negative urine cultures and lack of bacterial organisms within the biopsy, a common finding in pyelonephritis.2 Anecdotally, this response has been reported in reference texts7 but to our knowledge is not present in the primary literature. Other types of plasma cell related injury can be excluded by the presence of normal glomeruli and lack of tubular basement membrane thickening (MIDD and amyloid). No tubular intraepithelial cell crystal accumulation or increased lysosomal bodies were present excluding proximal tubulopathy. However, brightly eosinophilic, sharply demarcated crystalline structures of varied geometric shapes were focally present intermixed with abundant neutrophils in the distal tubular lumina, which stained exclusively for λ light chains, diagnostic of monoclonal lambda crystal deposits.

Both lambda and kappa light chains are normally filtered through the glomeruli, reabsorbed, and metabolized in proximal tubules. When present in excess, such as in plasma cell dyscrasias, the filtered load of abnormal light chains overwhelms the proximal tubular reabsorption capacity, potentially leading to a downstream precipitation as amorphous casts with tubular protein (Bence–Jones cast nephropathy) or crystallization.3 Cast nephropathy typically develops when the abnormal monoclonal light chains have an affinity for binding to Tamm–Horsfall protein (uromodulin) and precipitate, leading to obstruction of the distal convoluted tubules.8 In this case, interestingly, the crystalline material largely does not have incorporated Tamm–Horsfall protein. Previously described by Sethi et al.,5 pathologic casts in the setting of multiple myeloma may be myeloma (Bence–Jones) protein casts, light chain crystal casts, or rarely light chain amyloid casts.

Inflammation may be seen in association with light chain (Bence–Jones) casts in the distal tubules, but when present is usually composed of mononuclear cells and multinucleated foreign body giant cells. The inflammatory infiltrate may also involve the interstitium. In a typical case, the intraluminal inflammation is believed to develop from direct transmigration of inflammatory cells through the basement membrane into the tubular lumen.9,10

In the setting of multiple myeloma or other plasma cell dyscrasias, the abnormal monoclonal light chains may have unique conformational changes within the amino acid structure, which are believed to induce specific pathological changes in specific organs (heart, liver, kidney).11,12 Taking the abnormal light chains from a patient with cast nephropathy and injecting them into rats causes cast nephropathy in the rat kidneys, and similarly for amyloidosis and MIDD.11 Specific amino acid mutations have been identified that makes certain light chains more likely to be pathogenic to tissues causing disease, particularly in the light chain variable domain region.13–15 Under appropriate intraluminal conditions of pH, concentration, and flow rates, they may crystallize and are often resistant to proteolysis within cells. We speculate that, in the absence of active pyelonephritis, the neutrophil rich tubular response has developed because of the chemotactic properties of the unique monoclonal lambda light chain crystals within the renal tubules in this patient.

Light chains are known to have an effect on neutrophils under normal and disease-associated conditions. Polyclonal as well as monoclonal light chains, when tested in vitro, have been shown to inhibit neutrophil apoptosis and migration.16 Tamm–Horsfall protein, which is also involved in the cast nephropathy process, may also play a key role by activating granulocytes.17 In conjunction, one or both of these processes may contribute to an increased number and altered distribution of neutrophils when exposed to significant amounts of abnormal light chains under the appropriate conditions.

A neutrophil-rich reaction to monoclonal Bence–Jones proteins, in particular the predominantly tubular intraluminal crystalline deposits, has been rarely mentioned in the literature.7 The identification and distinction between acute pyelonephritis and crystal storing nephropathy with chemo-attractive properties is significant because of major hematologic work-up, treatment, and prognostic implications, in middle and older age patients.

Declaration of interest

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.