Psgn

Disclaimer: This information is intended for medical professionals and is not a substitute for clinical judgment, patient-specific assessment, or consultation with specialists. Always refer to the latest evidence-based guidelines and local protocols for patient care.

Overview

• Definition: Post-streptococcal glomerulonephritis (PSGN) is an acute nephritic syndrome characterized by inflammation of the glomeruli, typically occurring 1-4 weeks after an infection with specific nephritogenic strains of Group A Streptococcus (GAS), most commonly pharyngitis or impetigo. It is an immune-mediated disease, not a direct infection of the kidney.
• Epidemiology:
  • Incidence: Variable globally. More common in developing countries due to higher rates of GAS infections, particularly impetigo. Incidence has declined in developed countries.
  • Age: Primarily affects children aged 6-10 years, but can occur at any age. Infrequently seen in infants and the elderly.
  • Sex: Slightly more common in males than females.
  • Seasonal Variation: Follows seasonal patterns of GAS pharyngitis (winter/spring) or impetigo (summer/fall).
• Classification: PSGN is considered a form of acute diffuse proliferative glomerulonephritis. It is classified based on its etiology (post-streptococcal infection) rather than distinct subtypes.

Pathophysiology

• Mechanism: PSGN results from an immune response to specific GAS antigens. The leading theory involves the formation and deposition of immune complexes containing streptococcal antigens (e.g., streptococcal pyrogenic exotoxin B (SPE-B/NAPB), nephritis-associated plasmin receptor (NAPlr), streptokinase) in the glomerular basement membrane and mesangium. This deposition activates the complement cascade (primarily the alternative pathway, leading to consumption of C3), recruits inflammatory cells (neutrophils, monocytes, T-cells), and causes glomerular injury, leading to increased permeability and impaired filtration.
  • Antigenic Targets:
    • SPE-B (or its precursor, NAPB): A cationic cysteine proteinase found in nephritogenic streptococci. It has a strong affinity for the glomeruli and may act as an "in-situ" antigen.
    • NAPlr: Nephritis-associated plasmin receptor is a GAPDH-related protein that binds plasmin, potentially contributing to glomerular inflammation and injury.
• Risk Factors:
  • Recent infection with nephritogenic strains of GAS (e.g., M types 1, 2, 4, 12, 18, 25, 49, 57, 60 for pharyngitis; M types 2, 49, 57, 60 for pyoderma).
  • Age (children 6-10 years).
  • Crowded living conditions, poor hygiene, low socioeconomic status (predisposing to GAS infections).
  • Genetic predisposition (less well-defined, but some HLA associations suggested).
• Protective Factors:
  • Good hygiene and sanitation to prevent skin infections.
  • Access to healthcare for prompt diagnosis and treatment of GAS infections.
  • Note: While prompt antibiotic treatment of GAS pharyngitis prevents acute rheumatic fever, its efficacy in preventing PSGN, particularly after impetigo, is debated and not consistently proven.

Clinical Presentation

Signs and Symptoms

Typically appear 1-4 weeks after a streptococcal pharyngitis or 3-6 weeks after streptococcal impetigo. - Cardinal Features: * Hematuria: Gross (cola-colored, smoky, or reddish-brown urine) or microscopic. Present in nearly all cases. * Edema: Periorbital swelling (especially in the morning), facial puffiness, or dependent edema (legs, sacrum). Due to fluid retention. * Hypertension: Mild to severe, often associated with volume overload. * Oliguria: Reduced urine output, indicating decreased glomerular filtration. - Early Signs: * Facial/periorbital edema. * Darkening of urine. * Malaise, anorexia, mild abdominal pain, flank pain. - Advanced Signs: * Severe hypertension (with headache, visual disturbances, altered mental status suggestive of hypertensive encephalopathy). * Signs of acute heart failure (dyspnea, orthopnea, crackles on lung auscultation) due to severe volume overload. * Uremic symptoms (nausea, vomiting, lethargy) if acute kidney injury is severe. - Atypical Presentations: * Subclinical disease with only microscopic hematuria and mild proteinuria, discovered incidentally. * Isolated hematuria without edema or hypertension. * Rapidly progressive glomerulonephritis (RPGN) picture, though rare.

Physical Examination

• Inspection:
  • Periorbital edema, facial puffiness.
  • Dependent edema (pitting edema) in lower extremities or sacrum.
  • Jugular venous distention (JVD) if significant volume overload.
  • Skin lesions (e.g., impetigo, cellulitis) if recent skin infection was the source.
• Palpation:
  • Pitting edema.
  • Tachycardia, possibly with an S3 gallop if heart failure is present.
• Special Tests:
  • Blood Pressure Measurement: Crucial for detecting hypertension. Monitor regularly.
  • Weight: Daily weights to monitor fluid status.
  • Fluid balance assessment: Input/output charting.

Diagnostic Approach

History Taking

• Key Questions:
  • Recent sore throat (within 1-3 weeks)? Was it treated with antibiotics?
  • Recent skin infection (impetigo, scabies, infected wounds) (within 3-6 weeks)?
  • Onset and character of urine changes (color, frequency, volume)?
  • Presence of edema (location, timing)?
  • Symptoms of hypertension (headache, blurred vision, dizziness)?
  • Symptoms of fluid overload (shortness of breath, orthopnea, chest pain)?
  • Family history of kidney disease?
• Red Flags:
  • Severe hypertension (e.g., BP >99th percentile for age/sex/height, or >180/120 mmHg in adults).
  • Altered mental status, seizures (suggesting hypertensive encephalopathy).
  • Acute onset of dyspnea, orthopnea (suggesting pulmonary edema/heart failure).
  • Anuria or severe oliguria.

Laboratory Tests

• First-Line:
  • Urinalysis with Microscopy:
    • Gross or microscopic hematuria (typically >10 RBCs/HPF).
    • Dysmorphic RBCs and RBC casts: Highly suggestive of glomerular bleeding.
    • Mild to moderate proteinuria (<3.5 g/day, often <1 g/day), rarely nephrotic range.
    • Specific gravity may be high if oliguric.
  • Serum Creatinine and Blood Urea Nitrogen (BUN): Elevated due to decreased GFR.
  • Serum Electrolytes: May show hyponatremia (dilutional), hyperkalemia, or metabolic acidosis if severe AKI.
  • Complement Levels:
    • C3: Markedly decreased in >90% of cases due to alternative pathway activation. Usually normalizes within 6-8 weeks. Persistent low C3 beyond 8-12 weeks warrants investigation for other glomerulonephritides (e.g., membranoproliferative GN, lupus nephritis).
    • C4: Typically normal in PSGN.
  • Streptococcal Antibody Titers:
    • Antistreptolysin O (ASO) titer: Elevated after streptococcal pharyngitis (peak 3-5 weeks post-infection, remains elevated for months). Less reliable after impetigo.
    • Anti-DNase B titer: Elevated after both pharyngitis and impetigo (more reliable for skin infections than ASO). Remains elevated longer than ASO.
    • Streptozyme test: A panel of several streptococcal antibodies (ASO, anti-DNase B, anti-hyaluronidase, anti-streptokinase, anti-nicotinamide adenine dinucleotidase). Useful if multiple antibodies are needed.
  • Throat Culture/Rapid Strep Test: May be positive if active pharyngitis is present, but often negative by the time GN symptoms appear.
  • Skin Culture: If active impetigo or skin lesions are present.
• Confirmatory:
  • Renal Biopsy: Generally not required for diagnosis if the clinical presentation is classic, and serological evidence of recent streptococcal infection with low C3 and normal C4 is present.
    • Indications for biopsy: Atypical presentation (e.g., absence of prior strep infection, rapid progressive renal failure, persistent severe proteinuria/nephrotic syndrome, persistent hypocomplementemia beyond 8-12 weeks, age <2 years or >60 years).
    • Histological findings: Diffuse endocapillary proliferation with neutrophil and monocyte infiltration. Immunofluorescence shows granular deposits of IgG and C3 in a "starry-sky" pattern (mesangial and capillary loops). Electron microscopy reveals characteristic large, dome-shaped subepithelial electron-dense deposits (known as "humps").
• Monitoring:
  • Daily electrolytes, BUN, creatinine during acute phase.
  • Regular monitoring of blood pressure.
  • Urinalysis (hematuria, proteinuria) until resolution.
  • Repeat C3 levels at 6-8 weeks to confirm normalization.

Imaging

• Recommended:
  • Renal Ultrasound: To assess kidney size, rule out obstructive uropathy, or identify other renal pathologies. Kidneys are usually normal in size or slightly enlarged acutely.
  • Chest X-ray: If symptoms of pulmonary edema or cardiomegaly are present due to severe volume overload.
• Advanced: Not typically required for PSGN diagnosis.

Management

Acute Management

Primarily supportive, focusing on managing fluid overload, hypertension, and acute kidney injury. - Immediate: * Assess airway, breathing, circulation (ABCs). * Vital signs monitoring (BP, heart rate, respiratory rate, oxygen saturation). * Establish intravenous access if needed for medication or severe volume overload. - Stabilization: * Fluid and Sodium Restriction: Strict intake restrictions, typically 300-500 mL/m²/day plus urine output, to manage edema and hypertension. Sodium restriction to <2 g/day. * Diuretics: * Loop diuretics (e.g., Furosemide): Initial dose 0.5-1 mg/kg IV or PO (children), 20-40 mg IV or PO (adults). May require higher doses (up to 2-4 mg/kg IV, maximum 6 mg/kg/dose in children or 160-200 mg in adults) in patients with significant renal impairment. Monitor electrolytes, especially potassium. * Antihypertensives: For sustained hypertension. * Calcium Channel Blockers (e.g., Nifedipine, Amlodipine): Nifedipine 0.25-0.5 mg/kg PO/SL for acute severe hypertension (onset within 15-30 min). Amlodipine 0.1-0.3 mg/kg/day PO once daily for sustained control. * ACE Inhibitors/ARBs: Use with caution due to risk of hyperkalemia and acute kidney injury in setting of volume depletion or severe renal impairment. Generally avoided in the acute phase of PSGN unless other agents are ineffective and renal function is closely monitored. * Other agents: Hydralazine IV (0.1-0.2 mg/kg IV) or Labetalol IV (0.2-1 mg/kg IV) for hypertensive emergency. * Antibiotics: If there is evidence of an active streptococcal infection (positive throat/skin culture, or strong clinical suspicion) treat with appropriate antibiotics (e.g., Penicillin V 250 mg PO BID-TID for 10 days, or Amoxicillin 500 mg PO TID for 10 days, or Cephalexin for penicillin allergy). This primarily treats the infection, but its role in preventing PSGN progression once established is minimal. - Emergency: * Hypertensive Encephalopathy: Characterized by severe hypertension, headache, seizures, altered mental status. Requires rapid but controlled lowering of blood pressure using IV agents (e.g., labetalol, nicardipine, fenoldopam). Goal to reduce BP by 25% in first hour. * Acute Pulmonary Edema/Heart Failure: Requires aggressive diuresis (high-dose IV furosemide), oxygen, and possibly vasodilators. * Severe Hyperkalemia/Metabolic Acidosis/Uremia: May necessitate emergent dialysis.

Chronic Management

• Pharmacological:
  • No specific immunosuppressive therapy is indicated for typical PSGN.
  • Continued management of hypertension with oral antihypertensives as needed until blood pressure normalizes.
  • Diuretics as needed for persistent edema.
• Non-pharmacological:
  • Dietary sodium restriction.
  • Fluid restriction if ongoing edema or hypertension.
  • Regular physical activity (as tolerated after recovery).
• Monitoring:
  • Long-term monitoring of blood pressure, urinalysis (for persistent hematuria or proteinuria), and renal function (BUN, creatinine) for at least 6-12 months.
  • If proteinuria or hypertension persists beyond 6-12 months, consider further evaluation and potential referral to a nephrologist.

Treatment Algorithms

• First-Line:
  1. Confirm diagnosis (clinical, labs: UA, electrolytes, BUN/Cr, C3, strep titers).
  2. Supportive care: fluid/sodium restriction.
  3. Manage complications: Diuretics for fluid overload, antihypertensives for hypertension.
  4. Antibiotics for active streptococcal infection (if present).
• Second-Line:
  1. If severe AKI, intractable fluid overload, severe electrolyte imbalances, or uremic symptoms: initiate renal replacement therapy (dialysis).
• Refractory Cases:
  1. If clinical course is atypical (e.g., no evidence of strep, persistent low C3 >8-12 weeks, rapid decline in renal function, nephrotic range proteinuria), consider renal biopsy to rule out other forms of glomerulonephritis (e.g., RPGN, IgA nephropathy, membranoproliferative GN, lupus nephritis).
  2. Management will then be directed by the biopsy findings.

Complications

• Common:
  • Hypertension (up to 80% of patients).
  • Fluid overload and edema.
  • Acute kidney injury (mild to moderate).
• Serious:
  • Hypertensive Encephalopathy: With seizures, severe headache, confusion.
  • Acute Heart Failure with Pulmonary Edema: Due to severe volume overload.
  • Severe Hyperkalemia and Metabolic Acidosis: Requiring urgent intervention or dialysis.
  • Uremia: Requiring dialysis.
  • Acute Stroke: Secondary to severe uncontrolled hypertension.
• Long-term:
  • Most children recover completely.
  • Rarely, especially in adults or those with severe initial kidney injury, PSGN can lead to:
    • Persistent microscopic hematuria or proteinuria.
    • Persistent hypertension.
    • Progressive chronic kidney disease (CKD), though this is uncommon, estimated <1-2% in children, but higher in adults (up to 10-30% in some cohorts).

Prognosis

• Factors:
  • Age: Prognosis is generally excellent in children, with >95% achieving complete clinical and biochemical recovery. Adults have a higher risk of persistent renal abnormalities and progression to CKD.
  • Severity of initial presentation: Severe AKI, persistent proteinuria, or uncontrolled hypertension may indicate a slightly poorer prognosis.
  • Histological findings: Less common, but specific biopsy findings (e.g., crescents, severe interstitial fibrosis) can influence prognosis.
• Survival: Excellent in children. Mortality is rare and usually due to complications like severe hypertension, heart failure, or severe electrolyte imbalances.
• Quality of Life: Most patients return to their baseline quality of life after recovery. Long-term follow-up is important to detect and manage any persistent issues.

Prevention

• Primary:
  • Treatment of Streptococcal Pharyngitis: Prompt and adequate antibiotic treatment (e.g., 10 days of penicillin V) prevents acute rheumatic fever, but its efficacy in preventing PSGN after pharyngitis is not definitively established in all studies, although it is often recommended for source control.
  • Treatment of Streptococcal Impetigo: Antibiotic treatment of impetigo generally does not prevent PSGN. Therefore, preventing impetigo through good hygiene, sanitation, and addressing crowded living conditions is paramount.
• Secondary: Early diagnosis and supportive management of PSGN to prevent acute life-threatening complications.
• Tertiary: Long-term follow-up to monitor for and manage persistent hypertension, proteinuria, or signs of progressive CKD.

Special Populations

• Pediatric: Most common population. Generally has an excellent prognosis with complete recovery. Management focuses on careful fluid and electrolyte balance due to their smaller total body water and higher risk of acute complications.
• Geriatric: Less common, but tends to have a more severe clinical course and a higher likelihood of progression to CKD or persistent renal dysfunction. May have more comorbidities that complicate management. Atypical presentations are more common, often requiring renal biopsy.
• Pregnancy: Extremely rare. Management must consider both maternal and fetal well-being. Close monitoring of blood pressure and renal function is critical. Antihypertensives safe for pregnancy should be chosen (e.g., labetalol, nifedipine, methyldopa). Avoid ACE inhibitors/ARBs.
• Comorbidities:
  • Pre-existing Chronic Kidney Disease: Patients with underlying CKD may experience a more rapid and severe decline in renal function.
  • Diabetes Mellitus: Increased risk of complications and potentially slower recovery.
  • Cardiac Disease: Higher risk of severe fluid overload and heart failure.

Clinical Pearls

• Diagnostic:
  • The classic triad of hematuria (cola-colored urine), edema, and hypertension in a child following a recent strep infection is highly suggestive of PSGN.
  • Depressed C3 and normal C4 complement levels are a key diagnostic hallmark. If C3 remains low beyond 8-12 weeks, reconsider the diagnosis.
  • ASO titer is useful for pharyngitis, anti-DNase B for impetigo.
  • Renal biopsy is generally not needed for classic cases, reserving it for atypical presentations or diagnostic uncertainty.
• Treatment:
  • Supportive care is the cornerstone. There is no role for immunosuppressive therapy (e.g., corticosteroids).
  • Aggressive management of hypertension and fluid overload is crucial to prevent life-threatening complications like hypertensive encephalopathy and pulmonary edema.
  • Strict fluid and sodium restriction.
  • Monitor electrolytes closely, especially with diuretic use or AKI.
• Pitfalls:
  • Over-diuresis: Can lead to hypovolemia and worsen AKI, especially in patients who are already oliguric.
  • Delaying treatment of severe hypertension: Can result in devastating neurological or cardiac complications.
  • Misinterpreting persistent low C3: Suggests an alternative diagnosis, such as membranoproliferative glomerulonephritis or lupus nephritis, requiring further investigation.
  • Assuming PSGN is benign in adults: Adults have a higher risk of long-term complications and require careful follow-up.

Recent Updates

• Guidelines: Current KDIGO (Kidney Disease: Improving Global Outcomes) guidelines provide a framework for the diagnosis and management of glomerulonephritis, including PSGN. These guidelines emphasize supportive care and close monitoring for complications.
• Evidence: Ongoing research continues to refine the understanding of nephritogenic streptococcal antigens and the specific immune mechanisms involved in PSGN pathogenesis. This may lead to more targeted diagnostic or preventive strategies in the future.
• Controversies: The precise role of antibiotics in preventing PSGN following streptococcal pharyngitis, and especially impetigo, remains an area of debate. While antibiotics are crucial for preventing rheumatic fever, their impact on PSGN incidence appears less pronounced, particularly for skin infections.

Key References

• Guidelines:
  • KDIGO 2021 Clinical Practice Guideline for the Management of Glomerular Diseases. (Specific chapters on acute GN).
• Studies/Reviews:
  • Pais P, D'Agati VD, D'Agati VD, et al. Poststreptococcal Glomerulonephritis. N Engl J Med. 2017 Mar 9;376(10):976-978.
  • Eison TM, Ault BH, Jones DP, et al. Post-streptococcal acute glomerulonephritis in children: clinical features and pathogenesis. Pediatr Nephrol. 2011 Feb;26(2):165-80.
  • Laddha K, Anirudh NS. Post-streptococcal glomerulonephritis: A review. Indian J Nephrol. 2019 Mar-Apr;29(2):107-111.
  • Rodriguez-Iturbe B, Musser JM. The current state of poststreptococcal glomerulonephritis. J Am Soc Nephrol. 2008 Sep;19(9):1855-64.