Nephrotic syndrome Study Guide

📖 Core Concepts Nephrotic syndrome = loss of large amounts of protein in urine → low serum albumin, high lipids, edema. Glomerular filtration barrier damage enlarges pores → albumin, antithrombin III, immunoglobulins spill into urine. Under‑fill hypothesis: hypoalbuminemia ↓ oncotic pressure → fluid shifts into interstitium → edema. Over‑fill hypothesis: sodium‑water retention via epithelial Na⁺ channel activation → intravascular volume expansion → edema. Primary vs. secondary: Primary (minimal change, FSGS, membranous, MPGN, RPGN) – disease originates in the kidney. Secondary (diabetes, lupus, amyloidosis) – systemic disease damages glomeruli. 📌 Must Remember Proteinuria threshold: > 3.5 g / 1.73 m² / day or urine protein‑to‑creatinine ratio > 200–400 mg/mmol. Hypoalbuminemia: serum albumin < 2.5 g/dL. Hyperlipidemia: ↑ LDL & VLDL; contributes to atherosclerotic risk. Edema types: periorbital (morning), pitting leg edema, pleural effusion, ascites, anasarca. Complications: thromboembolism (loss of antithrombin III), infections (loss of Ig’s), AKI (hypovolemia), pulmonary edema. Most common cause in children: Minimal change disease (≈ 66 %). Most common cause in adults: FSGS (adults) / membranous & MPGN (epidemiology varies). First‑line edema therapy: loop diuretics + sodium restriction (1–2 g/day). ACE inhibitor = BP control + ↓ proteinuria. 🔄 Key Processes Pathogenesis of proteinuria Glomerular barrier injury → ↑ pore size → albumin leaks → hypoalbuminemia → ↓ plasma oncotic pressure → edema (under‑fill). Simultaneously, hypoalbuminemia → renal tubular Na⁺ reabsorption ↑ → fluid retention (over‑fill). Edema management workflow ↓ dietary Na (≤ 2 g) → loop diuretic (furosemide) → assess response. If refractory: IV albumin 25 % (4 h) → repeat diuretic dose. Monitor weight, urine output, electrolytes. Thromboembolism prevention Identify high‑risk (serum albumin < 2 g/dL, immobilization). → prophylactic LMWH. Diagnostic algorithm Urine dipstick → quantify proteinuria (U‑PCR). Serum albumin, lipids, creatinine. If adult or steroid‑resistant child → renal biopsy → direct therapy. 🔍 Key Comparisons Under‑fill vs. Over‑fill edema Under‑fill: caused by low oncotic pressure → intravascular volume ↓ → renin‑angiotensin activation. Over‑fill: primary Na⁺‑water retention → intravascular volume ↑ → edema despite normal/low oncotic pressure. Minimal change disease vs. FSGS MCD: children, normal LM, steroid‑responsive, excellent prognosis. FSGS: adults, segmental sclerosis on LM, steroid‑resistant, progressive to ESRD. Primary vs. Secondary nephrotic syndrome Primary: kidney‑limited pathology, often treated with immunosuppression. Secondary: treat underlying systemic disease (e.g., tight glucose control in diabetic nephropathy). ⚠️ Common Misunderstandings “All edema is due to low albumin.” → Over‑fill mechanisms can produce edema even with modest hypoalbuminemia. “Foamy urine equals nephrotic syndrome.” → Foamy urine can appear with any proteinuria; must confirm > 3.5 g/day. “Statins cure hyperlipidemia in nephrotic syndrome.” → They lower lipids but do not address the underlying protein loss; diet remains essential. 🧠 Mental Models / Intuition “Leak‑Leak‑Swelling”: Think of the glomerulus as a sieve that suddenly gets bigger holes → albumin leaks out → water follows → swelling. “Two‑hit edema model”: First hit = loss of oncotic pressure; second hit = kidney’s sodium‑retaining response → the bigger the combined hit, the more severe the edema. 🚩 Exceptions & Edge Cases Nephrotic-range proteinuria with normal albumin → suspect secondary causes (diabetes, amyloidosis) that do not cause hypoalbuminemia. Children with steroid‑resistant nephrotic syndrome → biopsy is indicated early (not only after 6 weeks). Pregnant patients → fluid restriction may be hazardous; focus on albumin infusion and careful diuresis. 📍 When to Use Which Diuretic choice: Loop diuretic (furosemide) → first line; add thiazide if diuretic resistance. Albumin infusion: Use when diuretics fail and intravascular volume is critically low (e.g., hypotension, AKI risk). Anticoagulation: LMWH prophylaxis when serum albumin < 2 g/dL or prior thrombotic event. Immunosuppression: Steroids for MCD; calcineurin inhibitors or rituximab for steroid‑resistant FSGS; cyclophosphamide for membranous disease. 👀 Patterns to Recognize Proteinuria + hypoalbuminemia + hyperlipidemia → classic nephrotic syndrome. Rapid rise in creatinine + massive edema → think hypovolemia‑induced AKI (under‑fill). History of lupus, low complement → secondary lupus nephritis rather than primary. Urine dip‑negative for blood/casts + massive protein → glomerular barrier leak (nephrotic) vs. tubular proteinuria (e.g., multiple myeloma). 🗂️ Exam Traps “Proteinuria > 3 g/24 h is sufficient for diagnosis.” – The accepted cutoff is ≥ 3.5 g/24 h or U‑PCR > 200 mg/mmol. “All nephrotic patients need statins.” – Statins are added only if dietary measures fail to reach target lipid levels. “Furosemide alone cures edema.” – In over‑fill states, albumin infusion before diuretic is often required to mobilize intravascular volume. “Nephrotic syndrome always presents with hematuria.” – Typically no hematuria or casts; presence suggests another glomerulopathy. “Kidney biopsy is mandatory in every case.” – Reserved for adults or steroid‑resistant children; not first‑line in classic pediatric MCD.