Renal · Glomerular Diseases
The facts most likely to be tested
The hallmark histologic finding of Rapidly Progressive Glomerulonephritis (RPGN) is the presence of crescents in the Bowman space, composed of fibrin and macrophages.
Goodpasture syndrome (Anti-GBM disease) presents with the classic triad of hemoptysis, hematuria, and linear IgG deposits along the glomerular basement membrane.
Granulomatosis with polyangiitis (GPA) is associated with c-ANCA (PR3-ANCA) positivity and typically involves the upper respiratory tract, lungs, and kidneys.
Microscopic polyangiitis is associated with p-ANCA (MPO-ANCA) positivity and lacks the granulomatous inflammation seen in GPA.
Immune complex-mediated RPGN (Type II) is characterized by granular immunofluorescence and is often a complication of post-streptococcal glomerulonephritis, SLE, or IgA nephropathy.
Pauci-immune RPGN (Type III) is the most common form and is characterized by a lack of immunofluorescence staining on renal biopsy.
Urgent renal biopsy is the definitive diagnostic step for RPGN, and high-dose pulse corticosteroids are the immediate first-line treatment to prevent irreversible renal failure.
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A 32-year-old male presents to the emergency department with hemoptysis and dyspnea for the past week. He reports dark-colored urine and decreased urinary output. Physical examination reveals bilateral crackles on lung auscultation and pitting edema in the lower extremities. Laboratory studies show a serum creatinine of 4.2 mg/dL and a urinalysis demonstrating dysmorphic red blood cells and red cell casts. A chest X-ray shows bilateral pulmonary infiltrates.
What is the most likely diagnosis and the expected finding on immunofluorescence?
Goodpasture syndrome; linear IgG deposits.
The patient presents with pulmonary-renal syndrome (Goodpasture syndrome), which is a type of RPGN characterized by anti-GBM antibodies that produce linear IgG deposits on immunofluorescence.
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Etiology / Epidemiology
Defined by rapid decline in GFR (>50% over 3 months) due to crescent formation in Bowman's space.
Clinical Manifestations
Presents as nephritic syndrome with hematuria, RBC casts, and oliguria.
Diagnosis
Renal biopsy is the gold standard showing crescents in >50% of glomeruli.
Treatment
Immediate pulse-dose methylprednisolone followed by cyclophosphamide.
Prognosis
High risk of end-stage renal disease; requires urgent intervention to prevent permanent damage.
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Epidemiology & Etiology
Classified into three types: Anti-GBM disease (Goodpasture syndrome), Immune-complex mediated (SLE, post-infectious), and Pauci-immune (ANCA-associated vasculitis). It is a medical emergency requiring rapid identification to prevent irreversible fibrosis. Incidence peaks in adults aged 50-70, though Goodpasture syndrome shows a bimodal distribution.
Pertinent Anatomy
The primary site of injury is the glomerular capillary tuft and the surrounding Bowman's capsule. Disruption of the glomerular basement membrane allows fibrin and inflammatory cells to enter the urinary space.
Pathophysiology
Severe glomerular injury leads to the leakage of plasma proteins and fibrin into the Bowman's space. This triggers the proliferation of parietal epithelial cells and the infiltration of macrophages, forming crescents. These structures compress the capillary tuft, leading to a rapid decline in GFR and eventual glomerular sclerosis.
Clinical Manifestations
Patients present with nephritic syndrome: hematuria (often 'cola-colored' urine), RBC casts, and variable proteinuria. Hypertension and edema are common. Goodpasture syndrome specifically presents with the triad of hemoptysis, hematuria, and anti-GBM antibodies.
Diagnosis
Renal biopsy is the gold standard diagnostic test, revealing crescents in >50% of glomeruli. Serologic workup is mandatory: anti-GBM antibodies, ANCA, and ANA/C3/C4 levels to differentiate the three types. Urinalysis will consistently show dysmorphic RBCs and RBC casts.
Treatment
Initial management requires pulse-dose methylprednisolone followed by a tapering course of oral steroids. Cyclophosphamide is the standard cytotoxic agent for induction. Plasmapheresis is indicated for Goodpasture syndrome or severe pulmonary hemorrhage. Avoid nephrotoxic agents during the acute phase.
Prognosis
Without treatment, progression to end-stage renal disease occurs within weeks to months. Serum creatinine at presentation is the most significant predictor of long-term renal recovery. Patients require close monitoring of GFR and proteinuria.
Differential Diagnosis
Acute Tubular Necrosis: muddy brown casts, not RBC casts
Post-streptococcal GN: low C3 levels, history of pharyngitis
Lupus Nephritis: positive ANA and anti-dsDNA
IgA Nephropathy: recurrent hematuria after URI, no crescents
Interstitial Nephritis: eosinophiluria, drug-induced