Nephrotic Syndrome I and II

Question 1

Glomerulus

Answer 1

•Anastomosing capillaries lined by fenestrated endothelium, supported by mesangium, surrounded by Bowman’s capsule, with two layers of epithelium (visceral and parietal).

Question 2

Glomerular Capillary Wall

Answer 2

1. Thin layer of fenestrated endothelium.
2. Glomerular basement membrane (lamina densa, lamina rara interna and lamina rara externa), composed mostly of Type IV collagen.
3. Visceral epithelial cells (podocytes) – Interdigitating “foot” processes, separated by slit diaphragm (filtration slit).

Question 3

Mesangium

Answer 3

1. Supports the capillary loops.
2. Consists of cells and matrix

Question 4

Bowman’s Capsule

Answer 4

•Lined by parietal epithelial cells.

Question 5

Nephrotic Syndrome

Answer 5

Clinical condition related to dysfunction of glomerular podocyte. Four key components:

1. Proteinuria > 3.5 gm/24 hours.
2. Hypoalbuminemia
3. Hyperlipidemia and lipiduria
4. Edema

Question 6

Acute Nephritic Syndrome

Answer 6

• Clinical condition associated with glomerular capillary dysfunction/inflammation (active glomerulonephritis).
• Main clinical features: Hematuria, proteinuria, increased blood pressure, edema, increased serum creatinine, and active urinary sediment.
• Active urinary sediment – Red blood cells and casts (made of red blood cells, white blood cells and/or epithelial cells) detected in the urine; indicates active glomerulonephritis

•Rapidly progressive glomerulonephritis - Severe form of acute nephritic syndrome with rapid rise in serum creatinine (renal emergency).

Question 7

Persistent Asymptomatic Urine Abnormalities

Answer 7

•Usually subnephrotic range proteinuria (< 3.5 gm/24 hours) or persistent/recurrent microscopic hematuria.

Question 8

Renal Failure

Answer 8

•Elevated serum creatinine.

1. Acute – Glomerular, vascular or tubulointerstitial disease.
2. Chronic – Advanced renal disease, usually irreversible, due to a variety of primary diseases.

Question 9

Clinical Presentations Leading to Renal Biopsy

Answer 9

1. Nephrotic Syndrome
2. Acute Nephritic Syndrome
3. Persistent asymptomatic urine abnormalities
4. Renal Failure

Question 10

Three Modalities of Renal Biopsy Examination

Answer 10

1. Light Microscopy
2. Immunofluorescence Microscopy
3. Electron Microscopy

•All samples must have cortex with glomeruli

Question 11

Light Microscopy

Answer 11

1. Multiple level sections of formalin-fixed tissue cut and mounted on glass slides.
2. Basic stain: Hematoxylin and Eosin (H&E)

•General stain, good for inflammatory cells

3. Special stains:

•Periodic Acid Schiff (PAS)

• Mesangium, basement membranes

•trichrome

• Fibrosis, necrosis

•Jones silver stain

• Basement Membranes

Question 12

Immunofluorescence Microscopy

Answer 12

1. Used to detect presence of immunoglobulin and complement proteins.
2. Multiple level sections of frozen tissue cut and mounted on glass slides.
3. Proteins detected: IgG, IgM, IgA, C3, C4, C1q, fibrinogen, albumin, kappa light chain, and lambda light chain.

• Immunofluorescence Microscopy (IF) Antibodies used:

– Immunoglobulins:

• Heavy chains: IgA, IgG, IgM
• Light chains: kappa, lambda

– Complement: C3, C4, C1q

– Fibrin/fibrinogen

• Marker of severe injury (necrosis, crescents)

– Albumin

• Good barometer for background staining - “Stickiness” factor

Question 13

Electron Microscopy

Answer 13

1. Transmission electron microscope is used to examine ultrastructure of renal tissue.
2. Tissue fixed and embedded in hard epoxy resin; ultrathin sections cut using diamond blade; sections mounted on a grid and examined using electron microscope.

Question 14

Answer 14

Question 15

Three Proposed Mechanisms of Immune Complex Formation

Answer 15

•Some forms of renal disease are caused by antigen-antibody complexes.

1. Antigen-antibody complexes form in the blood, circulate to the kidney and are then deposited into renal tissue.
2. A circulating antigen is first deposited into the kidney, and the recognizing antibody then binds to the planted antigen.
3. A protein normally present in renal tissue acts as an auto-antigen, and the recognizing antibody binds to this intrinsic renal protein.

Question 16

Mechanisms of Renal Injury

Answer 16

1. Antigen-antibody complexes activate the complement cascade.
2. Some results of complement activation:
   a. Elaboration of cytokines and chemokines.
   b. Recruitment of inflammatory cells.
   c. Damage to renal tissues from cell lysis, actions of inflammatory mediators, activation of digestive enzymes, etc.
3. Inflammatory type of injury more severe in diseases that cause acute nephritis vs nephrotic syndrome.

Question 17

Pathophysiology of Nephrotic Syndrome

Answer 17

1. Glomerular Proteinuria
2. Hypoalbuminemia
3. Edema
4. Hyperlipidemia and Lipiduria

Question 18

Glomerular Proteinuria

Answer 18

– Increased filtration of macromolecules across glomerular capillary

– Due to abnormalities in podocyte

– Albumin – Principal urinary protein

• Clotting inhibitors
• Transferrin
• Vitamin D binding protein

Question 19

Hypoalbuminemia

Answer 19

– Consequent to urinary albumin loss

– Hepatic albumin synthesis increases but is unable to sufficiently replete serum levels

– Serum albumin levels are low

• Usually <2 g/dl (nl 3.5-5.5 g/dL)

Question 20

Edema

Answer 20

– Hypoalbuminemia causes egress of fluid into interstitial space

• Due to decreased plasma oncotic pressure

– Stimulation of the Renin-Angiotensin system

• aldosterone release causing marked sodium retention
• sympathetic stimulation
• reduced natiuretic peptide release

– Soft dependent, pitting edema

Question 21

Hyperlipidemia and Lipiduria

Answer 21

• Hyperlipidemia

– Decreased oncotic pressure stimulates hepatic lipoprotein synthesis

• Manifests as hypercholesterolemia, hypertrigliceridemia
• Lipiduria

– Lipid in urine becomes entrapped within protein material in renal tubules “lipid casts”

– Enclosed by cytoplasmic membrane of degenerated cells = “oval fat body”

• Cholesterol in oval fat bodies appear as maltese crosses under polarized light

Question 22

Complications of Nephrotic Syndrome

Answer 22

A. Altered coagulation

1. Thromboembolism - Typically seen with >10 grams of proteinuria.
   a. Increased hepatic production of procoagulation factors.
   b. Anticoagulant factors lost through glomerular capillaries (anti-thrombin III).
   c. Concomitant volume depletion from diuretic therapy + reduced oncotic pressure in the vasculature leads to hemoconcentration and increased platelet aggregation.
   d. Thrombus formation
   i. Predilection for renal vein thrombosis (likely due to loss of fluid across the glomerulus and ensuing hemoconcentration in the postglomerular circulation).

B. Infection

1. Due to immunoglobulin loss in the urine.
2. Common infections: Staphylococcus and Streptococcus pneumoniae

Question 23

Generalized Treatment of Nephrotic Syndrome (Non specific Therapy)

Answer 23

A. Renin-angiotensin system: All should be treated with ACE inhibitors (ACEi) and or angiotensin receptor blockers (ARB) to reduce intraglomerular capillary pressure and reduce proteinuria.

B. Diuresis: Loop diuretics for edema, low sodium diet (<2g/day).

C. Strict blood pressure control: Goal <130/80 mm/Hg.

D. Statin: Treatment of hyperlipidemia (Statin = HMG-CoA reductase inhibitor).

Question 24

Causes of Nephrotic Syndrome

Answer 24

1. Primary Glomerular Diseases
   - Membranous Nephropathy
   - Minimal Change Disease
   - Primary Focal Segmental Glomerulosclerosis
   - Idiopathic/Autoimmune Membranoproliferative Glomerulonephritis
2. Secondary Systemic Diseases
   - Diabetic Nephropathy
   - Amyloidosis
   - Systemic Lupus Erythematosus

Question 25

Minimal Change Disease (MCD) - Epidemiology

Answer 25

•Primary glomerular disease 1. Most common cause of nephrotic syndrome in children; (90% in children 10 years with increased percentage typically FSGS). 2. Accounts for 10-15% of nephrotic syndrome in adults.

Question 26

Minimal Change Disease (MCD) - Etiology

Answer 26

•Primary glomerular disease 1. Idiopathic 2. Drugs – NSAIDs 3. Neoplasm – Hodgkin’s disease, lymphoma, leukemia

Question 27

Minimal Change Disease (MCD) - Pathogenesis

Answer 27

•Primary glomerular disease 1. Exact cause unknown; key feature: Podocyte injury a. Systemic T cell dysfunction thought to result in production of a glomerular permeability factor that injures podocytes leading to foot process effacement and proteinuria. 2. May follow respiratory infection or viral illness.

Question 28

Minimal Change Disease (MCD) - Renal Biopsy Findings

Answer 28

•Primary glomerular disease 1. Light Microscopy a. Normal appearance (i.e. “minimal” changes) 2. Immunofluorescence – Negative 3. Electron Microscopy a. Diffuse effacement of podocyte foot processes b. No immune complexes; normal glomerular basement membrane

Question 29

Minimal Change Disease (MCD) - Clinical Course

Answer 29

•Primary glomerular disease 1. Historically, untreated MCD was associated with risk of mortality due to infection and risk of thromboembolism. 2. Generally responsive to steroid therapy (90% of children respond) with good prognosis; no progression to chronic renal disease. 3. Patients may have acute renal failure due to tubular injury (acute tubular necrosis)

Question 30

Minimal Change Disease (MCD) - Treatment

Answer 30

•Primary glomerular disease 1. All should receive nonspecific therapy outlined above (section VII). 2. High dose steroids (prednisone). 3. Cyclophosphamide in patients who are steroid-dependent (i.e. steroids cannot be stopped without relapse in nephrotic syndrome). 4. Cyclosporine in patients who are resistant (no or poor response) to steroids; consider re-biopsy as diagnosis may be FSGS.

Question 31

Focal Segmental Glomerulosclerosis (FSGS) - Epidemiology

Answer 31

•Primary glomerular disease 1. Most common cause of nephrotic syndrome in adults (~ 35% of all biopsies for nephrotic syndrome). 2. Second most common to minimal change disease in children. 3. Increased incidence in African-Americans and males.

Question 32

Focal Segmental Glomerulosclerosis (FSGS) - Etiology

Answer 32

•Primary glomerular disease 1. Primary - Idiopathic and genetic/familial a. Familial forms are associated with genes encoding slit diaphragm proteins in the foot process of the podocyte, including nephrin, podocin, TRPC6, alphaactinin-4. 2. Secondary – Heterogeneous, occurs in many forms of renal injury and systemic disease. a. Special associations: Loss of renal mass, obesity, HIV, Sickle Cell disease, drugs.

Question 33

Focal Segmental Glomerulosclerosis (FSGS) - Pathogenesis

Answer 33

•Primary glomerular disease 1. Primary – Mechanisms of podocyte injury: a. Immune dysregulation - Systemic T-cell dysfunction, similar to MCD (same disease continuum but reduced responsiveness to therapy). b. Genetic mutations of podocyte proteins (as above) c. May involve presence of a circulating toxin which is supported by the rapidity of recurrent disease following renal transplant. 2. Secondary – Mechanisms of podocyte injury: a. Hyperfiltration and increased glomerular capillary hypertension (in reduced renal mass, obesity, Sickle Cell disease). b. Direct injury to the podocyte from virus (HIV).

Question 34

Focal Segmental Glomerulosclerosis (FSGS) - Renal Biopsy Findings

Answer 34

1. Light Microscopy a. Focal glomeruli show sclerosis (scarring) of a segment of the glomerular capillary tuft. b. Sclerotic lesions may have accumulation of collagen/matrix material, foam cells and/or proteinaceous material (hyaline). 2. Immunofluorescence a. No specific immune complex deposition. b. Non-specific trapping of immunoglobulins and complement (usually IgM and C3) in areas of sclerosis. 3. Electron Microscopy a. No immune deposits. b. Obliteration of a segment of the glomerulus by accumulation of matrix, cells and plasma protein material (hyaline). `c. Diffuse podocyte foot process effacement in primary FSGS; variable/patchy effacement in secondary FSGS.

Question 35

Focal Segmental Glomerulosclerosis (FSGS) - Clinical Course

Answer 35

•Primary glomerular disease 1. Primary FSGS may present with acute or insidious onset. a. Hematuria in 30% of patients, hypertension, variable degrees of reduced function. 2. Secondary FSGS always presents with insidious onset. a. Presents more often with nephrotic range proteinuria (\>3.5 g) rather than full nephrotic syndrome. 3. Untreated primary FSGS follows a progressive course to ESRD, rate of spontaneous remission 10g), reduced renal function (elevated creatinine), and presence of tubulointerstitial fibrosis. 4. Risk factors for progression include high level proteinuria (i.e. \>10g), reduced renal function (elevated creatinine), and presence of tubulointerstitial fibrosis. 5. Primary FSGS may recur after transplant, sometimes within days. a. See diffuse podocyte injury by EM first; then sclerotic lesions appear by light microscopy as recurrent disease progresses.

Question 36

Focal Segmental Glomerulosclerosis (FSGS) - Treatment

Answer 36

•Primary glomerular disease 1. Primary FSGS – Treatment similar to MCD a. All should receive nonspecific therapy outlined above (section VII). b. High dose prednisone. - Less likely to respond vs MCD. c. Cyclophosphamide or cyclosporine in patients who are steroid dependent and/or resistant. d. If no response to above therapies, may have familial FSGS with mutations in slit diaphragm proteins. 2. Secondary FSGS a. Nonspecific therapy - ACE inhibitors and angiotensin receptor blockers. b. Treatment of underlying disease (i.e. HIV)

Question 37

Membranous Neuropathy - Epidemiology

Answer 37

•Primary glomerular disease 1. Second most common cause of nephrotic syndrome in adults. 2. Occurs in all ethnic groups, most common in men \>40 yrs.

Question 38

Membranous Neuropathy - Etiology

Answer 38

•Primary glomerular disease 1. Primary/idiopathic (70%) and secondary (30%) forms. 2. Associations in secondary membranous: a. Drugs (penicillamine, captopril, gold, NSAIDs) b. Malignancy (carcinomas, melanoma) c. Systemic lupus erythematosus d. Infections (Hepatitis B, lesser extent Hepatitis C)

Question 39

Membranous Neuropathy - Pathogenesis

Answer 39

•Primary glomerular disease 1. Immune complex mediated disease a. Primary – Often due to circulating IgG antibodies directed against antigen expressed on the podocyte foot process (antigen = Type-M phospholipase A2 receptor). b. Secondary - Antigens = Viral proteins, tumor proteins, drug related substances, etc. 2. Immune complex formation activates complement cascade. a. Assembly of C5b-9 (membrane attack complex) inserts into podocyte plasma membrane resulting in complement-mediated podocyte injury. 3. Proteinuria – Due to podocyte foot process effacement (dysfunction of slit diaphragm) and loss of podocytes (apoptosis, necrosis, and detachment from the underlying basement membrane).

Question 40

Membranous Neuropathy - Renal Biopsy Findings

Answer 40

1. Light Microscopy a. Diffuse thickening of the glomerular capillary loops. b. Small “spikes” of glomerular basement membrane material sometimes visible by Jones silver stain. 2. Immunofluorescence a. Fine granular immune deposits along the glomerular capillary walls. b. Usually IgG, C3, kappa and lambda. 3. Electron Microscopy a. Numerous, small electron dense immune deposits along the subepithelial aspect of glomerular basement membrane. b. Reactive “spikes” of glomerular basement membrane material form between deposits. c. Diffuse podocyte foot process effacement.

Question 41

Membranous Neuropathy - Clinical Course

Answer 41

•Primary glomerular disease 1. Spontaneous remission occurs in up to 30% patients at 5 years; spontaneous partial remission (\<2 grams proteinuria/day) occurs in up to 40% patients at 5 years 2. Progression to ESRD in 40% at 15 years if untreated. 3. Risk factors for progression: a. Older age of onset, male \> females, increased serum creatinine, \>8 grams of proteinuria at presentation, presence of tubulointerstitial fibrosis on biopsy

Question 42

Membranous Neuropathy - Treatment

Answer 42

•Primary glomerular disease 1. All should receive nonspecific therapy outlined above 2. Immune-targeted therapy if there are risk factors for progression or patient remains symptomatic on ACEi/ARB/loops/diet. a. Cyclophosphamide + prednisone administered over 6 months. b. Cyclosporine + low dose prednisone as an alternative to those who fail or cannot tolerate cyclophosphamide. c. Rituximab (monoclonal antibody to CD20) will likely replace Cyclophosphamide as first-line treatment

Question 43

Diabetic Neuropathy - Epidemiology and Clinical Presentation

Answer 43

•Secondary - systemic disease 1. Most common systemic illness to cause nephrotic syndrome and most common cause of ESRD in the US. 2. Occurs in both Type I and Type II diabetes, often with genetic susceptibility. 3. Common in Hispanic, Native American and Black populations.

Question 44

Diabetic Neuropathy - Pathogenesis

Answer 44

•Secondary - systemic disease 1. Metabolic – Hyperglycemia and pro-inflammatory mediators cause biochemical derangements of glomeruli leading to increased synthesis of matrix proteins and pro-fibrotic growth factors. a. Nonenzymatic glycosylation (covalent binding of glucose) to proteins in glomerulus contributes to glomerulopathy. 2. Hemodynamic – Hyperfiltration leading to increased glomerular capillary pressure and glomerular hypertrophy.

Question 45

Diabetic Neuropathy - Renal Biopsy Findings

Answer 45

•Secondary - systemic disease 1. Light Microscopy a. Glomeruli – Diffusely thickened glomerular basement membranes, increased mesangial matrix leads to formation of large nodules comprised of matrix material (Kimmelstiel-Wilson nodules). b. Tubules/interstitium – Thick tubular basement membranes, progressive fibrosis. c. Vessels – Intimal sclerosis of arteries (arteriosclerosis); hyalinosis of arterioles. 2. Immunofluorescence a. No specific immunoglobulin or complement deposition. b. Pseudolinear staining of glomerular and tubular basement membranes with IgG and albumin. i. Due to “stickiness” of basement membranes. 3. Electron Microscopy a. Diffuse thickening of glomerular basement membranes due to increased amount of lamina densa. b. No immune deposits. c. Increased mesangial matrix and mesangial cells, often forming nodules of matrix material. d. Variable podocyte foot process effacement (more severe in advanced disease).

Question 46

Diabetic Neuropathy - Clinical Course

Answer 46

•Secondary - systemic disease 1. Patients present with proteinuria: a. Early - Leakage of small amounts of albumin (microalbuminuria), often asymptomatic. b. Late – Overt proteinuria with development of nephrotic syndrome. May take 10-20 years to develop. 2. Progression depends on blood sugar control. In many patients, progressive scarring leads to ESRD.

Question 47

Diabetic Neuropathy - Treatment

Answer 47

•Secondary - systemic disease 1. Nonspecific treatment outlined above (section VII). 2. Strict blood sugar control – Oral hypoglycemics and/or insulin. 3. Kidney-pancreas transplant – Definitive treatment for type I DM.

Question 48

Amyloidosis - Definition and Epidemiology

Answer 48

1. Group of diseases characterized by extracellular deposition of beta-sheet fibrils (abnormally folded protein) within kidney 2. Cause of nephrotic syndrome in adults.

Question 49

Amyloidosis - Pathophysiology

Answer 49

•Secondary - systemic disease 1. Many different types, most important for renal disease are Primary (AL) and Secondary (AA). a. AL (primary) – Seen in patients with plasma cell myeloma; the abnormal protein consists of monoclonal immunoglobulin light chains (often lambda). b. AA (systemic reactive) – Seen in patients with chronic inflammatory diseases (i.e. rheumatoid arthritis, inflammatory bowel disease, hepatitis, chronic pyogenic infections including IV drug users). i. Protein - Serum amyloid A protein

Question 50

Amyloidosis - Renal Biopsy Findings

Answer 50

•Secondary - systemic disease 1. Light Microscopy a. Amorphous, pale eosinophilic material irregularly distributed in mesangium and along glomerular capillary loops. b. Also can be present in vessels and interstitium. c. Special stain: Congo red – Amyloid stains salmon or red color and shows apple green birefringence under polarized light. 2. Immunofluorescence a. Variable; may see light chain restriction if AL type (i.e. staining only for kappa without lambda, if the amyloid consists of kappa light chains). 3. Electron Microscopy a. Deposition of haphazardly arranged fibrils within the mesangium and glomerular basement membrane. b. Variable podocyte foot process effacement.

Question 51

Amyloidosis - Clinical Course and Treatment

Answer 51

•Secondary - systemic disease 1. Poor prognosis, progression to end stage renal disease is common. 2. Treatment – Nonspecific therapy outlined in Section VII should be initiated in primary and secondary amyloidosis. a. Primary – Chemotherapy, peripheral blood stem cell transplant. b. Secondary – Treat the underlying disease.

Question 52

Answer 52

Amyloid

Question 53

Answer 53

Primary Amyloidosis