Kidney nontumor / medical renal

• Lupus nephritis (LN) is an immune complex mediated renal injury encountered in systemic lupus erythematosus (SLE)
• Associated with activation of the classical complement pathway and presents as glomerular, tubulointerstitial and vascular disease, significantly increasing the risk of death in systemic lupus erythematosus patients

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• Class I LN: normal urinalysis, no or minimal proteinuria, normal serum creatinine
• Class II LN: microhematuria or mild proteinuria
• Class III LN: hematuria and proteinuria, which may be accompanied by nephrotic syndrome, active urinary sediment, decreased glomerular filtration rate, less frequently hypertension, rarely renal insufficiency; reduced complements and positive anti-dsDNA antibody
• Class IV LN: hematuria, proteinuria with nephrotic syndrome, red blood cell casts, hypertension, decreased glomerular filtration rate and renal failure are frequent; low complements, elevated anti-dsDNA antibody levels
• Class V LN: nephrotic range proteinuria, reduced complements, positive anti-dsDNA antibody
• Silent LN: kidney biopsy with class III, IV or V without any clinical evidence of kidney disease (UpToDate: Lupus Nephritis - Diagnosis and Classification [Accessed 21 April 2023])

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• LN class I: normal glomeruli by light microscopy
• LN class II: mesangial hypercellularity or mesangial matrix expansion
• LN classes III - IV: lesions may be active (endocapillary or extracapillary proliferation) or chronic (sclerosing)
  • Wire loop deposits, hyaline microthrombi, membranoproliferative lesions
  • Fibrinoid necrosis and karyorrhexis may be present
• LN class V: thickening of the glomerular capillary walls, microspikes and domes may be associated with any mesangial alterations
• LN class VI: extensive glomerular sclerosis
• Lupus podocytopathy: diffuse and severe foot process effacement in the absence of subendothelial or subepithelial immune deposits
• Tubulointerstitial disease: observed in all LN classes, active in LN classes III and IV consisting of lymphocytic interstitial inflammation with plasma cells, monocytes / macrophages and edema
• Vascular lesions: uncomplicated vascular immune deposits, noninflammatory necrotizing vasculopathy, vasculitis, thrombotic microangiopathy, vascular thrombi with recanalization in lupus anticoagulant syndrome
• LN activity and chronicity scoring system modified in 2018 and is based on scoring of 1 (< 25% of glomeruli), 2 (25 - 50% of glomeruli) and 3 (> 50% of glomeruli) (Kidney Int 2018;93:789)
• LN activity index
  1. Endocapillary proliferation
  2. Neutrophils / karyorrhexis
  3. Fibrinoid necrosis (score x 2)
  4. Hyaline deposits
  5. Cellular / fibrocellular crescents (score x 2)
  6. Interstitial inflammation (total score 0 - 24)
• LN chronicity index
  1. Total glomerulosclerosis score (global or segmental sclerosis; exclude sclerosis due to hypertension and normal aging)
  2. Fibrous crescents
  3. Tubular atrophy
  4. Interstitial fibrosis (total score 0 - 12)
• Reference: Clin Rev Allergy Immunol 2011;40:170

Contributed by Alexei Mikhailov, M.D., Ph.D.

Contributed by Alexei Mikhailov, M.D., Ph.D.

• Finalizes the classification of lupus nephritis for a given case
• Granular electron dense deposits (smaller in LN classes I - II and larger in classes III - IV) are seen in subepithelial, intramembranous, subendothelial and mesangial locations; locations are important in determining the LN class
• Subepithelial immune deposits show adjacent neomembrane formation
• Immune deposit substructure may be present
• Tubuloreticular inclusions: reticular aggregates of branching membranous tubule within the cisternae of endoplasmic reticulum found within the endothelial cells are useful in establishing the diagnosis of lupus erythematosus; are also found in other conditions with elevated levels of interferon (Pathology 2019;51:727)

Contributed by Alexei Mikhailov, M.D., Ph.D.

A 40 year old patient with a history of systemic lupus erythematosus is presenting with acute kidney injury and a new onset nephrotic syndrome. dsDNA is positive, C3 is 50 mg/dL, serum creatinine is 1.5 mg/dL and the urinary protein to creatinine ratio is 3,500 mg/g. Which of the following histological manifestations is most characteristic of the lupus nephritis class he is most likely presenting with?

1. Acute tubular injury
2. ANA reaction
3. Mesangial electron dense deposits
4. Microspikes and domes (neomembrane formation) seen with the Jones stain

D. Microspikes and domes (neomembrane formation) seen with the Jones stain. Neomembrane formation is most characteristic for lupus nephritis (LN) class V, even though it may sometimes be seen if subepithelial deposits are present in LN class IV. Answers A, B and C are incorrect because acute tubular injury, ANA reaction and mesangial electron dense deposits may be seen in any LN class.

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Reference: Systemic lupus erythematosus

Which of the following is most specific to lupus nephritis and helpful in differentiating between lupus nephritis and other etiologies?

1. Hyaline microthrombi
2. Mesangial proliferation
3. Positive immunostaining on the arterioles and tubular basement membranes with antibodies to IgG
4. Subendothelial electron dense deposits

C. Positive immunostaining on the arterioles and tubular basement membranes with antibodies to IgG. Extraglomerular immunostaining is very specific to lupus nephritis. Answer A is incorrect because hyaline microthrombi in the glomerular capillaries may also be seen in other conditions; for example, cryoglobulinemia (cryoglobulin plugs) and microthrombi consisting of monoclonal immunoglobulins in immunotactoid glomerulopathy. Answer B is incorrect because mesangial proliferation may be seen in a very wide range of etiologies, including minimal change disease, IgA nephropathy, focal segmental glomerulosclerosis (FSGS), Alport syndrome, etc. Answer D is incorrect because subendothelial electron dense deposits may be seen in any renal disease where immune complexes are formed (e.g., IgA nephropathy and postinfectious glomerulonephritis).

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Reference: Systemic lupus erythematosus

Biopsy is done on a patient with a history of systemic lupus erythematosus and nephrotic syndrome. Electron microscopy reveals the findings shown above. Which complication is the patient predisposed to?

1. Fibromuscular dysplasia of the renal artery
2. Oxalate nephropathy
3. Papillary necrosis
4. Renal vein thrombosis

D. Renal vein thrombosis. The risk of deep vein thrombosis, especially renal vein thrombosis, is increased in patients with lupus nephritis classes III, IV and V but especially in patients with membranous lupus nephritis (class V). Answer A is incorrect because fibromuscular dysplasia of the renal artery is a noninflammatory process leading to arterial stenosis. Answer B is incorrect because oxalate nephropathy is associated with deposition of calcium oxalate crystals in kidney tubules. The etiology includes primary hyperoxaluria, enteric hyperoxaluria (fat malabsorption) and ingestions (e.g., ethylene glycol poisoning). Answer C is incorrect because papillary necrosis is a complication of NSAID nephropathy.

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Reference: Systemic lupus erythematosus