Nephritic Syndrome

Basics

Description

Acute glomerulonephritis (AGN) is acute inflammatory damage to glomerulus, associated with:
- Abrupt onset of hematuria with or without RBC casts
- Acute renal failure manifested by edema, hypertension, azotemia, decline in urine output
- Variable proteinuria
- Active urine sediment (RBC casts)
Exact mechanism of AGN unclear:
- Combination of autoimmune reactivity to specific antigens at renal glomeruli
- Characterized by crescent formation secondary to nonspecific injury at the glomerular wall

Etiology

Poststreptococcal glomerulonephritis (PSGN):
- A postinfectious cause of acute nephritic syndrome, resulting from group A β-hemolytic streptococci
- Considered a nonsuppurative complication (antibiotic treatment does not prevent this complication)
- Occurs when immune complexes create hump-shaped subepithelial deposits in renal glomeruli
- Most commonly affects patients between ages 3–15 yr but can occur at any age
- Incidence of nephritis is 5–10% after pharyngitis and 25% after skin infections
- Consider PSGN in the setting of new-onset proteinuria, RBC casts, edema, and any recent infection
- Latent period between infection and onset of nephritis helps differentiate between PSGN and IgA nephropathy (IgA-N):
  - 1–3 wk in pharyngeal infection
  - 2–4 wk in cutaneous infection
- Renal biopsy is usually not necessary for diagnosis
- Low complement (C3) for 6–8 wk
- Can progress to severe renal failure if underlying infection goes untreated
- Prognosis:
  - Excellent; >95% recover spontaneously with normalization of renal function within 6–8 wk, even with dialysis
  - Hematuria usually resolves in 3–6 mo
  - Transient nephrotic phase in 20% of patients during resolution of illness
  - End-stage renal disease occurs <5%
  - Rapidly progressive glomerulonephritis (RPGN) is rare, occurring in <1% cases
  - Most cases resolve spontaneously with no long-term sequelae
Other infectious sources of glomerulonephritis (GN):
- Sepsis, pneumonia, endocarditis, viruses, HIV
- Pulmonary, intra-abdominal, or cutaneous infections
- Syphilis, leprosy, schistosomiasis, and malaria
- Goal: Treat underlying infection
Hepatitis virus–related glomerular disease:
- Can present with either nephritic or nephrotic symptoms
- Causes membranoproliferative GN
- Complements remain low indefinitely (compared to PSGN)
Noninfectious causes of GN (due to immune complex formation):
- Systematic lupus erythematosus, Henoch–Schönlein purpura, vasculitis, Wegener granulomatosis
- Goodpasture syndrome
IgA-N:
- Most common cause of AGN (>25%) worldwide
- Antibody–antigen causes immune complex deposition of IgA and C3
- Complement levels are usually normal
- IgA-N has different presentations:
  - Gross hematuria following upper respiratory infection (URI)
  - Microscopic hematuria with proteinuria
  - Hematuria during viral illness or after exercise
  - Prognosis is related to serum creatinine, BP, and proteinuria
  - 50% of patients with proteinuria may develop progressive renal disease
  - ACE inhibitors or angiotensin-receptor blockers (ARBs) may help
RPGN:
- Certain patients with AGN may progress rapidly to renal failure
- Hallmarks are crescents on renal biopsy
Hereditary nephritis:
- Alport syndrome

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