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Renal Involvement in Systemic Diseases

Q: What changes are detected in glomerular ultrastructure by electron microscopy in systemic lupus erythematosus?

Electron microscopy reveals immune deposits and specific inclusions in lupus nephritis: Immune deposits — Located in the mesangium and along the glomerular basement membrane (subendothelial, subepithelial, and intramembranous).Virus-like particles — Found in the endothelium of capillaries. The specific location of deposits along the basement membrane determines the clinicomorphological form of glomerulonephritis.

Q: What components form cellular crescents within the glomeruli in rapidly progressive glomerulonephritis?

Cellular crescents in rapidly progressive glomerulonephritis are formed by inflammatory infiltrating cells and components of Bowman's capsule: Proliferating epithelium — Cells of the parietal layer of Bowman's capsule (podocytes and parietal epithelial cells).Macrophages — Cells migrating into the site of inflammation.Fibrin strands — Protein structures escaping through capillary ruptures.Fibroblasts — Joining the cellular component during further disease progression.

Q: What specific morphological changes (types of glomerulosclerosis) develop in the kidneys in diabetes mellitus?

Diabetes mellitus leads to diabetic intracapillary glomerulosclerosis (Kimmelstiel-Wilson syndrome). The microscopic patterns include: Nodular glomerulosclerosis — Mesangial cell proliferation with matrix expansion forming round, homogenous, PAS-positive eosinophilic nodules.Diffuse glomerulosclerosis — Diffuse thickening of capillary basement membranes and mesangial expansion (the most common variant).Exudative lesions — Such as 'fibrin caps' and 'capsular drops'. Thickening of the capillary basement membrane is also an obligatory component.

Q: Which systemic diseases are most commonly accompanied by severe glomerular injury?

Glomerular injury can accompany many congenital, metabolic, and immunologic disorders. However, in systemic lupus erythematosus (SLE) and diabetes mellitus, renal injury is a primary clinical manifestation that determines prognosis.

Q: What is the paradox of vascular lesions in IgA vasculitis (Henoch-Schönlein purpura)?

The paradox is that despite prominent necrotizing small-vessel vasculitis of the dermis and gastrointestinal hemorrhages, true vasculitis within the renal parenchyma itself is extremely rare.

Q: How does immunofluorescence microscopy confirm renal involvement in IgA vasculitis?

The key diagnostic feature is the detection of immunoglobulin A (IgA) deposits in the glomerular mesangium, sometimes accompanied by IgG and complement component C3. This pattern is identical to isolated IgA nephropathy.

Q: What is the renal morphology in bacterial endocarditis depending on disease severity?

Mild endocarditis shows focal or segmental necrotizing glomerulonephritis. More severe cases progress to diffuse proliferative glomerulonephritis, and a rapidly progressive course leads to extensive crescent formation.

For medical students2 min readUpdated 2026-10-10

Glomerular injury is a predictable consequence of many immunological, metabolic, and congenital systemic diseases. In conditions such as systemic lupus erythematosus or diabetes mellitus, nephropathy becomes a major clinical manifestation that determines the patient's prognosis.

Purpura incidenceRenal involvement occurs in 1/3 of patients with IgA vasculitis (Henoch-Schönlein purpura).

IgA vasculitis markerImmunofluorescence microscopy reveals IgA deposits in the glomerular mesangium.

EndocarditisCauses immune-complex glomerulonephritis due to circulating bacterial antigens.

Rare findingUnlike the skin and GI tract, true vasculitis within the kidneys themselves is extremely rare in IgA vasculitis.

Leading symptomIn SLE and diabetes mellitus, renal injury is one of the primary clinical manifestations.

Systemic Lupus Erythematosus (SLE)

In systemic lupus erythematosus, renal involvement is characterized by a wide variety of clinical and morphological forms. Patients frequently present with recurrent microhematuria or gross hematuria. The condition may manifest as acute nephritis or overt nephrotic syndrome. Disease progression inevitably leads to persistent hypertension and chronic kidney disease.

Histologically, four main variants of glomerular changes are distinguished in lupus nephritis:

Mesangial lupus nephritis.
Focal glomerulonephritis.
Diffuse proliferative glomerulonephritis.
Diffuse membranous glomerulonephritis.

IgA Vasculitis (Henoch-Schönlein Purpura)

The disease is characterized by a classic clinical triad of extrarenal manifestations. First, there is skin involvement over the extensor surfaces of the upper and lower extremities, as well as the buttocks. Morphologically, the skin reveals subepidermal hemorrhages and necrotizing vasculitis of small dermal vessels. Second, gastrointestinal involvement (abdominal syndrome) includes severe abdominal pain, vomiting, and GI bleeding. Third, joint involvement presents as non-migratory arthralgia.

Renal involvement occurs in one-third of patients and presents with gross or microscopic hematuria, proteinuria, and nephrotic syndrome. The histological picture varies from mesangioproliferative changes to membranoproliferative glomerulonephritis. Some adult patients are diagnosed with severe crescentic glomerulonephritis. It is important to note: unlike the prominent vascular injury in the skin and GI tract, true vasculitis within the kidneys themselves is extremely rare.

Immunofluorescence microscopy is used for diagnosis. The key feature is the deposition of IgA (sometimes alongside IgG and the C3 complement fraction) in the glomerular mesangium. This distribution of deposits is identical to that seen in IgA nephropathy, leading to the hypothesis that they represent the same disease spectrum.

Bacterial Endocarditis

Renal involvement in infective endocarditis is pathogenetically a form of immune-complex glomerulonephritis. Glomerular injury is initiated by circulating bacterial antigen-antibody complexes.

Clinically, hematuria and proteinuria of varying severity are most characteristic. However, the development of classic acute nephritis is atypical, and rapidly progressive glomerulonephritis is rare.

In mild cases, focal or segmental necrotizing glomerulonephritis develops.
In more severe cases, diffuse proliferative glomerulonephritis occurs.
With rapidly progressive glomerulonephritis, multiple crescents form within the glomeruli.

Mnemonic

To remember the clinical features of IgA vasculitis (Henoch-Schönlein purpura), use the rule "SKS + Kidneys": Skin (vasculitis and purpura), Kidney/GI (abdominal syndrome), Sjoints (non-migratory arthralgia). And remember that renal involvement joins this triad in 1/3 of patients.

Frequently asked questions

What classes of lupus nephritis are distinguished in the modern ISN/RPS morphological classification?

The modern ISN/RPS morphological classification defines six classes of lupus nephritis:

Class I — Minimal mesangial lupus nephritis.
Class II — Mesangial proliferative lupus nephritis.
Class III — Focal lupus nephritis (active and sclerosing, <50% of glomeruli).
Class IV — Diffuse lupus nephritis (global or segmental, ≥50% of glomeruli).
Class V — Membranous lupus nephritis.
Class VI — Advanced sclerosing lupus nephritis (≥90% globally sclerosed glomeruli).

What changes are detected in glomerular ultrastructure by electron microscopy in systemic lupus erythematosus?

Electron microscopy reveals immune deposits and specific inclusions in lupus nephritis:

Immune deposits — Located in the mesangium and along the glomerular basement membrane (subendothelial, subepithelial, and intramembranous).
Virus-like particles — Found in the endothelium of capillaries.

The specific location of deposits along the basement membrane determines the clinicomorphological form of glomerulonephritis.

What components form cellular crescents within the glomeruli in rapidly progressive glomerulonephritis?

Cellular crescents in rapidly progressive glomerulonephritis are formed by inflammatory infiltrating cells and components of Bowman's capsule:

Proliferating epithelium — Cells of the parietal layer of Bowman's capsule (podocytes and parietal epithelial cells).
Macrophages — Cells migrating into the site of inflammation.
Fibrin strands — Protein structures escaping through capillary ruptures.
Fibroblasts — Joining the cellular component during further disease progression.

What specific morphological changes (types of glomerulosclerosis) develop in the kidneys in diabetes mellitus?

Diabetes mellitus leads to diabetic intracapillary glomerulosclerosis (Kimmelstiel-Wilson syndrome). The microscopic patterns include:

Nodular glomerulosclerosis — Mesangial cell proliferation with matrix expansion forming round, homogenous, PAS-positive eosinophilic nodules.
Diffuse glomerulosclerosis — Diffuse thickening of capillary basement membranes and mesangial expansion (the most common variant).
Exudative lesions — Such as 'fibrin caps' and 'capsular drops'.

Thickening of the capillary basement membrane is also an obligatory component.

Which systemic diseases are most commonly accompanied by severe glomerular injury?

Glomerular injury can accompany many congenital, metabolic, and immunologic disorders. However, in systemic lupus erythematosus (SLE) and diabetes mellitus, renal injury is a primary clinical manifestation that determines prognosis.

What is the paradox of vascular lesions in IgA vasculitis (Henoch-Schönlein purpura)?