Tubulointerstitial Diseases of the Kidney¶
Chapter 328 | Part 9: Disorders of the Kidney and Urinary Tract
KEY CLINICAL POINTS¶
- Acute interstitial nephritis (AIN) is often drug-induced (e.g., antibiotics, NSAIDs) or autoimmune (e.g., Sjögren’s, lupus), with features like fever, rash, and eosinophilia.
- Chronic tubulointerstitial nephritis (CIN) is associated with toxins (e.g., heavy metals, analgesics), infections (e.g., aristolochic acid), or autoimmune diseases, leading to fibrosis and tubular atrophy.
- Diagnosis relies on history, imaging, and biopsy; corticosteroids are used for severe cases, while discontinuation of offending agents is critical for recovery.
- Key differential diagnoses include autoimmune disorders (e.g., IgG4-related disease), infections (e.g., BK virus), and metabolic conditions (e.g., hypercalcemia).
- Management varies by cause: immunosuppressants for autoimmune etiologies, dialysis for acute kidney injury, and avoidance of nephrotoxic agents.
1. DEFINITION & OVERVIEW¶
Tubulointerstitial diseases involve inflammation or fibrosis of the renal interstitium and tubules, with relative sparing of glomeruli. Acute and chronic forms are distinguished by their etiology and progression. Acute TIN often presents with AKI, while chronic TIN manifests with tubular dysfunction and progressive renal failure.
Table 328-1: Classification of Causes of Tubulointerstitial Diseases¶
| Category | Causes |
|---|---|
| Acute Tubulointerstitial Disorders | Therapeutic agents (antibiotics, NSAIDs), Infections, Autoimmune (TINU, Sjögren’s), Obstructive (light chain casts) |
| Chronic Tubulointerstitial Disorders | Toxins (heavy metals, analgesics), Infections (BK virus, aristolochic acid), Autoimmune (IgG4-related disease), Metabolic (hypercalcemia) |
| Metabolic Disturbances | Hypercalcemia, Hyperuricemia, Hyperoxaluria, Cystinosis |
| Cystic and Hereditary Disorders | Polycystic kidney disease, Nephronophthisis, Medullary cystic kidney disease, Medullary sponge kidney |
1.1 Classification of Causes¶
Acute TIN: Drug-induced (antibiotics, NSAIDs), infections, autoimmune (e.g., TINU, Sjögren’s), or obstructive (e.g., light chain casts). Chronic TIN: Toxins (heavy metals, analgesics), infections (e.g., aristolochic acid), autoimmune diseases, or metabolic disorders (e.g., hypercalcemia).
1.2 Pathophysiology¶
Inflammation, fibrosis, and tubular atrophy result from immune-mediated injury, toxic insults, or metabolic disturbances. Drug-induced AIN involves immune-mediated tubular injury, while chronic CIN is linked to prolonged exposure to nephrotoxic agents or autoimmune processes.
2. EPIDEMIOLOGY¶
Acute TIN accounts for ~15% of unexplained AKI, but true incidence is likely higher due to underdiagnosis. Chronic CIN is more common in industrialized regions (e.g., analgesic nephropathy) or endemic areas (e.g., Balkan endemic nephropathy). Risk factors include drug exposure, autoimmune diseases, and environmental toxins.
2.1 Demographics¶
TINU predominantly affects females (3:1 ratio), with median age 15 years. Sjögren’s and lupus-related TIN are more common in adults. Chronic CIN is prevalent in agricultural communities and among patients with long-term analgesic use.
2.2 Risk Factors¶
Drug exposure (e.g., NSAIDs, antibiotics), autoimmune disorders (e.g., lupus, sarcoidosis), heavy metal toxicity (lead, cadmium), and metabolic disorders (hypercalcemia, hyperuricemia) are major risk factors.
3. ETIOLOGY & PATHOPHYSIOLOGY¶
Acute TIN is primarily immune-mediated (e.g., drug allergy, autoimmune diseases) or obstructive (e.g., crystal deposition). Chronic CIN results from prolonged exposure to toxins, metabolic derangements, or autoimmune processes. Pathogenesis involves inflammation, fibrosis, and tubular atrophy, with impaired renal concentrating ability and electrolyte disturbances.
3.1 Drug-Induced AIN¶
Antibiotics ( β -lactams, sulfonamides), NSAIDs, and immunomodulators (e.g., checkpoint inhibitors) trigger immune-mediated tubular injury. Proton pump inhibitors may contribute to subclinical interstitial nephritis.
3.2 Autoimmune and Inflammatory Causes¶
Sjögren’s, lupus, and IgG4-related disease cause granulomatous or lymphocytic interstitial nephritis. Sarcoidosis and tuberculosis may present with granulomatous lesions.
3.3 Metabolic and Toxin-Related Causes¶
Hypercalcemia, hyperuricemia, and aristolochic acid exposure lead to interstitial fibrosis and tubular damage. Chronic analgesic use (phenacetin) causes papillary necrosis and interstitial scarring.
4. CLINICAL FEATURES¶
Acute TIN presents with AKI, fever, rash, and eosinophilia. Chronic TIN manifests with tubular dysfunction (e.g., diabetes insipidus, Fanconi syndrome), proteinuria, and progressive renal failure. Complications include metabolic acidosis, hyperkalemia, and urothelial malignancy in aristolochic acid nephropathy.
4.1 Acute Presentation¶
Fever, rash, peripheral eosinophilia, oliguria, and rapid rise in creatinine. Atypical features include proteinuria without eosinophilia (e.g., NSAID-induced AIN).
4.2 Chronic Features¶
Polyuria, nocturia, hypokalemia, metabolic acidosis, and progressive azotemia. Fanconi syndrome features (glycosuria, aminoaciduria) may occur with proximal tubular damage.
5. DIFFERENTIAL DIAGNOSIS¶
Distinguish TIN from glomerular diseases (e.g., lupus nephritis), pyelonephritis, and obstructive uropathy. Consider autoimmune disorders (e.g., sarcoidosis, IgG4-related disease), infections (BK virus, tuberculosis), and metabolic causes (hypercalcemia, hyperuricemia).
5.1 Autoimmune Disorders¶
Sjögren’s, lupus, sarcoidosis, and IgG4-related disease may present with interstitial nephritis. TINU is associated with uveitis and systemic symptoms.
5.2 Infections¶
BK virus, tuberculosis, and fungal infections (e.g., histoplasmosis) can mimic TIN. Acute pyelonephritis may cause AKI but lacks interstitial inflammation.
6. INVESTIGATIONS & DIAGNOSIS¶
Urinalysis reveals pyuria, hematuria, and cellular casts. Imaging (ultrasound, CT) detects renal parenchymal changes. Biopsy shows interstitial inflammation, fibrosis, or granulomas. Serologic tests (e.g., anti-Ro/SS-A, ANCA) aid in autoimmune diagnoses.
Table 328-2: Indications for Corticosteroids and Immunosuppressives¶
| Absolute Indications | Relative Indications |
|---|---|
| Sjögren’s syndrome, Sarcoidosis, SLE interstitial nephritis, Adults with TINU, IgG4-related disease, Granulomatous IN | Drug-induced AIN with rapid renal failure, Diffuse infiltrates, Impending dialysis, Delayed recovery, Children with TINU, Postinfectious AIN with delayed recovery |
6.1 Laboratory Tests¶
Urinalysis: Pyuria, hematuria, and eosinophils. Serum creatinine, electrolytes, and BUN assess renal function. Urinary protein/creatinine ratio identifies proteinuria.
6.2 Imaging¶
Renal ultrasound detects echogenicity, cortical scarring, and pyelonephritis. CT or MRI may reveal obstructive lesions or calcifications (e.g., nephrocalcinosis).
6.3 Biopsy and Histology¶
Interstitium shows mononuclear cell infiltration, fibrosis, or granulomas. Acute AIN has eosinophilic infiltrates; chronic CIN shows fibrosis and tubular atrophy.
7. MANAGEMENT & TREATMENT¶
Discontinuation of offending agents is critical. Corticosteroids (e.g., prednisone) or immunosuppressants (e.g., azathioprine) are used for autoimmune or severe cases. Dialysis may be required for acute kidney injury. Long-term management includes monitoring for complications (e.g., hypercalcemia, urothelial cancer).
7.1 Acute Management¶
Withdraw offending drug, initiate corticosteroids for severe AIN, and manage complications (e.g., dialysis for AKI). For drug-induced AIN, volume repletion and drug cessation are key.
7.2 Chronic Management¶
Avoid nephrotoxic agents, treat underlying conditions (e.g., hypercalcemia, hyperuricemia), and monitor for progression. Lithium-associated nephropathy requires dose adjustment or discontinuation.
7.3 Specific Therapies¶
Allopurinol for hyperuricemia, rasburicase for tumor lysis, and chelation therapy for lead toxicity. For aristolochic acid nephropathy, surgical removal of affected kidneys may be necessary.
8. PROGNOSIS & COMPLICATIONS¶
Acute TIN often resolves with treatment, but chronic CIN may progress to ESRD. Complications include metabolic acidosis, hyperkalemia, urothelial cancer (aristolochic acid), and renal failure from drug toxicity. Early intervention improves outcomes.
8.1 Prognostic Factors¶
Severity of interstitial fibrosis, duration of exposure, and response to treatment. Early diagnosis and discontinuation of nephrotoxic agents improve prognosis.
8.2 Long-Term Risks¶
Progressive renal failure, electrolyte imbalances, and urothelial malignancy in aristolochic acid nephropathy. Chronic analgesic use increases risk of ESRD and urothelial cancer.
9. SPECIAL CONSIDERATIONS¶
Pregnancy: Avoid NSAIDs and certain immunosuppressants. Pediatrics: TINU is more common in children; monitor for relapses. Elderly: Increased risk of drug toxicity and chronic CIN. Agricultural workers: Exposure to heavy metals or toxins may contribute to CIN.
9.1 Pregnancy¶
Avoid NSAIDs and corticosteroids in early pregnancy. Monitor for drug-induced AIN and renal function changes.
9.2 Pediatrics¶
TINU is more common in children; treatment with corticosteroids is effective. Monitor for relapses and long-term renal function.
10. KEY POINTS & CLINICAL PEARLS¶
- Discontinue offending agents immediately for drug-induced AIN. 2. Corticosteroids are indicated for severe AIN or autoimmune causes. 3. Chronic CIN requires long-term management of underlying causes. 4. Monitor for complications like urothelial cancer in aristolochic acid nephropathy. 5. Early diagnosis and intervention improve outcomes in both acute and chronic tubulointerstitial diseases.