『A Comprehensive Clinical Guide to Glomerulonephritis for the Hospitalist』のカバーアート

A Comprehensive Clinical Guide to Glomerulonephritis for the Hospitalist

A Comprehensive Clinical Guide to Glomerulonephritis for the Hospitalist

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概要

 In this episode of Hospital Medicine Unplugged, we sprint through glomerulonephritis—recognize the nephritic syndrome, decode complement patterns and immunofluorescence clues, and manage diseases ranging from self-limited post-infectious GN to rapidly progressive crescentic disease. We start with the clinical syndrome of glomerulonephritis, defined by glomerular inflammation producing hematuria, hypertension, edema, and reduced kidney function. The classic picture is nephritic syndrome—tea- or cola-colored urine, oliguria, periorbital edema, and elevated blood pressure. At the microscopic level, RBC casts are the pathognomonic finding, proving that bleeding originates from the glomerulus rather than the urinary tract. Understanding disease requires revisiting the glomerular filtration barrier, composed of three layers: fenestrated endothelium, the glomerular basement membrane (GBM), and podocytes connected by slit diaphragms. This barrier normally filters plasma while retaining proteins. Podocytes are terminally differentiated and poorly regenerative, making them particularly vulnerable to immune-mediated injury. The core pathophysiology of GN is immune-mediated inflammation. Antibodies, immune complexes, and complement activation trigger inflammatory cascades within the glomerulus. This leads to endocapillary proliferation, mesangial expansion, and leukocyte infiltration, narrowing capillary lumens and lowering GFR. Capillary wall damage allows red blood cells to leak into urine, while the sudden decline in filtration drives sodium and water retention, producing hypertension and edema. Modern classification emphasizes pathogenesis rather than morphology, and most GN falls into five categories: • Immune-complex GN – granular immunoglobulin deposition (post-infectious GN, IgA nephropathy, lupus nephritis, MPGN) • Pauci-immune GN – minimal immune deposition, typically ANCA-associated vasculitis • Anti-GBM disease – linear IgG staining along the basement membrane • Monoclonal immunoglobulin GN – related to plasma cell disorders • C3 glomerulopathy – dominant complement deposition from alternative pathway dysregulation Epidemiology varies by disease. Post-streptococcal GN primarily affects children aged 2–10 years, particularly in developing regions. In contrast, IgA nephropathy is the most common primary glomerular disease worldwide and typically presents in young adults. Interestingly, epidemiology has shifted: childhood PSGN is declining, while adult infection-related GN—often associated with staphylococcal infections—is increasing. Clinical presentation depends on the underlying disease. Post-streptococcal GN typically occurs 1–12 weeks after a streptococcal infection, producing abrupt edema, hypertension, and hematuria. IgA nephropathy, in contrast, often presents with synpharyngitic hematuria—visible hematuria occurring simultaneously with an upper respiratory infection. The urinalysis is the diagnostic cornerstone. Key findings include dysmorphic red blood cells, RBC casts, and mild-to-moderate proteinuria. Complement levels help narrow the differential: • Low C3 and low C4: lupus nephritis, cryoglobulinemia, immune-complex MPGN • Low C3 with normal C4: post-infectious GN or C3 glomerulopathy • Normal complement: IgA nephropathy, ANCA-associated GN, anti-GBM disease A crucial teaching point: C3 should normalize within 6–8 weeks in post-streptococcal GN. Persistent hypocomplementemia suggests another diagnosis, such as lupus nephritis or MPGN. Additional testing includes ASO titers and anti-DNase B antibodies for streptococcal infection, autoimmune markers such as ANA and ANCA, and viral testing for hepatitis B, hepatitis C, and HIV. Imaging plays a limited role. Renal ultrasound typically shows normal or enlarged kidneys in acute GN, helping distinguish acute inflammatory disease from chronic kidney disease. When the diagnosis remains unclear—or when disease is severe—a kidney biopsy is essential. Histology reveals characteristic patterns: • Post-infectious GN: diffuse endocapillary proliferation with neutrophils • Crescents: severe injury indicating rapidly progressive GN • Electron microscopy: classic subepithelial “hump-shaped” deposits in post-infectious disease Immunofluorescence patterns guide classification: • Granular deposition: immune-complex GN • Linear IgG: anti-GBM disease • Pauci-immune: ANCA vasculitis • C3-dominant: C3 glomerulopathy Management begins with supportive care for all patients. Key interventions include: • Blood pressure control, ideally ≤120/70 mmHg with ACE inhibitors or ARBs • Sodium restriction (<2 g/day) • Diuretics for volume overload • Fluid restriction when necessary Treatment then becomes etiology-specific. For post-infectious GN, therapy is largely supportive because the disease usually resolves spontaneously. Edema typically improves within 1–2 weeks, and renal function normalizes ...
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