13.2 Tubulointerstitial, Vascular & Stone Disease

13.2 Tubulointerstitial, Vascular & Stone Disease

Quick Answer: Ischemic or toxic ATN causes muddy brown casts and rising creatinine after shock or nephrotoxins; AIN is drug allergy with eosinophils; pyelonephritis shows WBC casts and infection. Papillary necrosis clusters with sickle cell, analgesics, and diabetes. Renovascular disease is atheroma or FMD; malignant HTN produces onion-skin arterioles; HUS/TTP are thrombotic microangiopathies. Know stone chemistry (CaOx, struvite, uric acid, cystine) and ADPKD vs ARPKD genetics and presentations.

This section covers everything that is not primarily glomerular immune disease: tubules and interstitium, vessels, obstruction/stones, and cystic genetic disease. CBSE stems often give a drug, cast type, urine pH, or age/sex pattern and ask for the mechanism.

Acute Tubular Necrosis (ATN)

ATN is the most common intrinsic cause of acute kidney injury (AKI) in hospitalized patients. Damage centers on tubular epithelial cells—especially straight proximal tubule and thick ascending limb in the outer medulla, which are vulnerable to hypoxia.

Ischemic ATN

• Triggers: Prolonged prerenal states—shock, sepsis, major surgery, hemorrhage, severe heart failure—when hypoperfusion is severe or prolonged enough to injure tubules.
• Path: Patchy tubular epithelial necrosis, loss of brush border, tubular dilation, muddy brown granular casts and epithelial cell casts in urine.
• Course: Initiation → maintenance (oliguric or non-oliguric AKI, rising Cr) → recovery with tubular regeneration, often a polyuric phase as concentrating ability lags behind GFR recovery.
• BUN:Cr often falls toward ~10–15:1 (vs higher ratios in pure prerenal azotemia); FENa typically >2% once ATN is established (tubules cannot reabsorb Na well), contrasting with FENa <1% in prerenal states (unless on diuretics).

Toxic ATN

Exam pearl: Dipstick positive for blood without RBCs on microscopy → pigment (myoglobin or hemoglobin), not hematuria from glomeruli or stones.

Acute Interstitial Nephritis (AIN)

AIN is a hypersensitivity reaction in the tubulointerstitium, most often drug-induced.

• Classic drugs: β-lactam antibiotics (methicillin historically), other penicillins/cephalosporins, NSAIDs, sulfonamides, PPIs, rifampin, allopurinol, diuretics.
• Clinical triad (not always complete): fever, rash, eosinophilia; renal: rising Cr, sterile pyuria, WBC casts, eosinophiluria (Hansel/Wright stain historically taught).
• NSAID-related AIN may present later with nephrotic-range proteinuria (minimal change–like podocyte injury plus interstitial nephritis).
• Path: Interstitial edema and inflammation with eosinophils and lymphocytes; tubules may show invasion (tubulitis); glomeruli relatively spared.
• Management concept: Stop the drug; steroids sometimes used when recovery is slow—exams focus on recognition and culprit identification.

Acute Pyelonephritis and Chronic Tubulointerstitial Scarring

Acute pyelonephritis is infection of the renal parenchyma and pelvis, usually ascending from cystitis (E. coli and other enteric gram-negatives). Hematogenous seeding is less common (staph bacteremia).

• Clinical: Fever, CVA tenderness, dysuria/frequency, nausea; WBC casts indicate upper tract involvement (casts form in tubules).
• Complications: Abscess, papillary necrosis, sepsis, emphysematous pyelonephritis in diabetics (gas-forming organisms).
• Chronic pyelonephritis / reflux nephropathy: Repeated infection or vesicoureteral reflux → cortical scars over blunted calyces, thyroidization of tubules (colloid-like casts), interstitial fibrosis—can lead to CKD and hypertension.

Papillary Necrosis

Ischemic or toxic necrosis of the renal papillae. Sloughed papillae can cause obstruction, hematuria, or colic-like pain; IVP historically showed ring shadows/calyceal clubbing.

Classic associations (memorize):

• Sickle cell disease/trait (medullary hypoxia, sickling in vasa recta)
• Analgesic nephropathy (chronic phenacetin/combination analgesics; also NSAID overuse patterns)
• Diabetes mellitus
• Acute pyelonephritis
• Obstruction
• Sometimes listed with transplant rejection or severe ischemia

Mnemonic variants: POSTCARDS / SAAD (Sickle, Analgesic, Acute pyelo, Diabetes)—any complete list that includes sickle, analgesic, and diabetes is exam-safe.

Vascular Diseases of the Kidney

Renal Artery Stenosis (RAS)

Unilateral RAS can cause hypertension with the contralateral kidney showing hypertensive damage; the stenotic kidney is “protected” from high pressure but ischemic and renin-driving.

Malignant (Accelerated) Hypertension

• Very high BP with end-organ damage (encephalopathy, papilledema, AKI, microangiopathic hemolytic anemia).
• Vessels: Hyperplastic arteriolosclerosis—concentric, laminated onion-skin thickening of arterioles with luminal narrowing; fibrinoid necrosis of arterioles in hyperacute injury.
• Kidney: Petechial hemorrhages (“flea-bitten” cortex), ischemic wrinkling of glomeruli, TMA-like features possible.
• Differs from benign nephrosclerosis (hyaline arteriolosclerosis of long-standing essential HTN).

Thrombotic Microangiopathy: HUS and TTP Concepts

Thrombotic microangiopathy (TMA) = microvascular platelet thrombi, consumptive thrombocytopenia, microangiopathic hemolytic anemia (schistocytes), and organ ischemia.

Renal biopsy in TMA: fibrin thrombi in glomerular capillaries and arterioles, mesangiolysis, onion-skin arterioles in chronic disease. Exams test the ADAMTS13 vs Shiga toxin split more than subtle histology.

Other TMA associations: malignant HTN, scleroderma renal crisis, antiphospholipid syndrome, calcineurin inhibitors, pregnancy-related syndromes (HELLP overlap concepts).

Nephrolithiasis (Stone Types and Urine Chemistry)

Clinical: Flank pain radiating to groin, hematuria, CVA tenderness if infection. Hydronephrosis if obstructing. Thiazides reduce urinary calcium (useful for Ca stones); allopurinol/alkalinization strategies for uric acid; treat urease infection and remove staghorn for struvite; high fluid + alkalinization ± chelators for cystine.

Hydronephrosis and Obstruction

Hydronephrosis is dilation of the renal pelvis and calyces from urine outflow obstruction. Causes: stones, BPH, pregnancy (physiologic dilation more right-sided), tumors, strictures, posterior urethral valves (boys), vesicoureteral reflux (functional).

• Unilateral obstruction may spare GFR if contralateral kidney compensates; bilateral or solitary-kidney obstruction → AKI.
• Chronic obstruction → tubular atrophy, interstitial fibrosis, irreversible CKD; post-obstructive diuresis can occur after relief of bilateral obstruction.
• Imaging (US first-line) shows dilated collecting system; distinguish from cystic disease by communication of dilated calyces with pelvis.

Polycystic Kidney Disease: ADPKD vs ARPKD

ADPKD exam hooks: Adult with bilateral flank masses/HTN, family history, sudden worst headache → subarachnoid hemorrhage from berry aneurysm. ACEI often used for HTN. ARPKD hooks: Neonate with Potter sequence features if severe oligohydramnios, or child with portal HTN and renal disease.

Other cystic entities briefly: simple cysts (benign, common with age); acquired cystic disease of dialysis; medullary sponge kidney (benign collecting duct dilation, nephrocalcinosis/stones); multicystic dysplastic kidney (congenital nonfunctioning kidney with cysts—unilateral usually).

Putting Tubulointerstitial and Vascular Vignettes Together

Master these pattern matches, then add one mechanism sentence (renin drive, urease ammonia, Shiga toxin endothelium, polycystin cilia) for full credit on explanation-style reasoning even in multiple-choice form.

Chronic Tubulointerstitial Disease and Analgesic Nephropathy

Chronic interstitial nephritis presents with bland sediment, mild proteinuria (tubular, usually <1–2 g/day), concentrating defects, and gradual GFR loss. Causes include chronic obstruction, reflux, heavy metals, calcineurin inhibitors, lithium (also nephrogenic DI), hyperuricemia, and Balkan nephropathy–type toxins historically. Analgesic nephropathy from chronic combination analgesics produces interstitial scarring and a high rate of papillary necrosis; patients may pass tissue fragments and have sterile pyuria. On exams, long-term analgesic use plus papillary necrosis is a direct link.

Contrast Nephropathy and Prevention Logic

Iodinated contrast can cause a rise in creatinine within 24–72 hours, usually peaking by day 3–5 and recovering if baseline function allows. Mechanism is a mix of afferent arteriolar vasoconstriction (medullary ischemia) and direct tubular toxicity. Risk multiplies with CKD, diabetes, volume depletion, and high contrast load. Exam prevention themes: periprocedural volume expansion, hold metformin around exposure (lactic acidosis risk if AKI develops), and minimize contrast—not that every vignette needs management detail, but mechanism questions often contrast “toxic ATN” with ischemic ATN or AIN.

Integrating with Glomerular Disease (13.1)

A rising creatinine is not automatically “GN.” Use the urine sediment: muddy brown granular casts → ATN; WBC casts + drug rash → AIN; WBC casts + fever/CVA pain → pyelo; RBC casts → glomerular; crystals + colic → stones. Vascular crises (malignant HTN, TMA, bilateral RAS with ACEI) can mimic intrinsic renal failure without primary immune deposits. Keep 13.1 for deposit/IF logic and 13.2 for tubules, vessels, stones, and cysts—together they cover nearly all CBSE renal pathology stems outside pure electrolyte physiology.