Acute Tubulointerstitial Nephritis Flashcards
Acute Tubulointerstitial Nephritis
Epidemiology of Acute Tubulointerstitial Nephritis:
Prevalence of acute tubulointerstitial nephritis (ATIN) is increasing in recent years.
Overall prevalence of biopsy-proven ATIN is 2% to 5%.
Incidence conveys information about the risk of contracting the disease, whereas prevalence indicates how widespread the disease is.
Prevalence of biopsy-proven ATIN in patients with acute kidney injury (AKI) is 10% to 15%.
Acute Tubulointerstitial Nephritis
Pathogenesis of ATIN:
(3 suggested mechanisms)
- The inciting agent (i.e., infection or drug) acts as a hapten. That is, the inciting agent binds to an otherwise nonimmunogenic native kidney protein and renders it immunogenic.
- Antibodies made against the inciting agent cross-reacts with native kidney antigens.
- Circulating immune complexes formed against the inciting agent deposit into the kidney interstitium and induce an inflammatory immunologic response.
Acute Tubulointerstitial Nephritis
Pathogenesis of ATIN:
Immunologic response:
Predominantly cell mediated: kidney biopsy typically reveals predominant T-cell infiltrates in interstitium.
Hallmark of AIN: Inflammatory interstitial infiltrate of monocytes and lymphocytes (fewer eosinophils, plasma cells, and neutrophils) Interstitial edema Renal tubule separation Tubulitis Absence of glomerular or vascular pathology
Fibrotic changes may be seen as early as within 7-10 days Granuloma patterns can occur and commonly drug-related
Acute Tubulointerstitial Nephritis
Pathogenesis of ATIN:
Immunologic response:
Less commonly antibody mediated:
Most biopsies do not reveal immune complex deposits.
In some cases, immune complex deposits may be seen in tubular basement membranes (TBM)
Acute Tubulointerstitial Nephritis
Clinical Manifestations of ATIN
Classic triad of skin rash, leukocyturia, and fevers:
Not common; likely seen in <10% of cases
Classic triad is uncommonly seen in NSAIDS-induced ATIN.
More commonly seen with antibiotic-induced ATIN
Acute Tubulointerstitial Nephritis
Clinical Manifestations of ATIN
AKI:
Onset of kidney injury typically occurs within 10 to 20 days of exposure to inciting agent.
Kidney injury may occur within 2 to 3 days with re-exposure.
De novo kidney injury from a medication previously tolerated may be observed.
Acute Tubulointerstitial Nephritis
Clinical Manifestations of ATIN
Abnormal urinalysis: leukocytouria, microscopic or gross hematuria, eosinophiluria, white blood cell casts, granular casts, proteinuria. Red blood cell casts reported but rare.
Eosinophiluria:
Poor sensitivity (40% to 91%) and specificity (52% to 95%), but improved specificity if eosinophils is >5% of total leukocyturia.
test sensitivity is the ability of a test to correctly identify those with the disease (true positive rate), whereas test specificity is the ability of the test to correctly identify those without the disease (true negative rate).
Eosinophiluria may also be seen in urinary tract infections, prostatitis, bladder malignancy, and rapidly progressive glomerulonephritis.
Hansel stain for eosinophilia is preferred over Wright stain due to Hansel stain’s consistent sensitivity with varying urine pH.
Acute Tubulointerstitial Nephritis
Clinical Manifestations of ATIN
Proteinuria:
Typically nonnephrotic range (i.e., <1 g/d, or urine protein to creatinine ratio < 1 g/g)
LMW proteinuria predominance a.k.a. “tubular proteinuria”: albuminuria generally comprises less than 25% of total proteinuria.
May be nephrotic if associated with NSAIDS use.
Acute Tubulointerstitial Nephritis
Clinical Manifestations of ATIN
Blood tests:
Elevated serum creatinine (SCr),
leukocytosis with increased eosinophilia,
anemia, elevated erythrocyte sedimentation rate, transaminitis. Anti-neutrophil cytoplasmic antibody (ANCA) may be positive without associated glomerular disease.
Acute Tubulointerstitial Nephritis
Histopathology of ATIN
Light microscopy (LM):
Inflammatory infiltrates within the interstitium:
Infiltrative lesions can be diffuse, but often are patchy, predominating in the deep cortex and outer medulla. Inflammatory cells are mostly T-cells and monocytes, macrophages, and also plasma cells, eosinophils, and a few neutrophilic granulocytes
Acute Tubulointerstitial Nephritis
Histopathology of ATIN
Light microscopy (LM):
Tubulitis may be seen in ATIN.
Tubulitis refers to leukocytes and lymphocytes infiltration into tubular epithelium.
Acute Tubulointerstitial Nephritis
Histopathology of ATIN
Light microscopy (LM):
Granulomas may be seen in ATIN or CTIN associated with sarcoidosis,
Sjogren syndrome, granulomatous polyangiitits, infections (e.g., tuberculosis, leprosy, histoplasmosis, xanthogranulomatous pyelonephritis), crystals/foreign bodies (e.g., urate, oxalosis, recreational drug impurities), medications (e.g., sulfas, synthetic penicillins, NSAIDS, thiazides, levofloxacin).
Acute Tubulointerstitial Nephritis
Histopathology of ATIN
Immunofluorescent microscopy (IF) and electron microscopy (EM):
IF and EM are typically negative because most ATIN have no immune complex deposits.
Acute Tubulointerstitial Nephritis
Histopathology of ATIN
Immunofluorescent microscopy (IF) and electron microscopy (EM):
In some instances, antibodies may be formed linearly against antigens or drugs bound to tubular basement membrane (TBM) (e.g., methicillin, NSAIDS, phenytoin, allopurinol).
Acute Tubulointerstitial Nephritis
Histopathology of ATIN
Immunofluorescent microscopy (IF) and electron microscopy (EM):
Kidney biopsies from patients with AKI from hantavirus infection may reveal granular immune deposits along the TBM and within glomeruli in 50% of cases.
Acute Tubulointerstitial Nephritis
Diagnosis of ATIN
Gold standard: kidney biopsy
Urinalysis with abnormalities mentioned earlier
Acute Tubulointerstitial Nephritis
Diagnosis of ATIN
Gallium scan:
Gallium binds to lactoferrin on white blood cells and originally thought to identify conditions with high white blood cell count such as ATIN.
Poor sensitivity and specificity and not recommended for the diagnosis of ATIN
May also be positive in association with glomerular diseases, presumably with concurrent interstitial disease, pyelonephritis, atheroembolic disease, etc.
Acute Tubulointerstitial Nephritis
Causes of ATIN
85% to 95% of ATIN are either drug- (adults in the United States) or infection induced (children, developing countries).
Drugs (Allergic interstitial nephritis) (70-75%) • Antibiotics: 30-50% • Mean delay between drug start date and AKI is 10 days • Latent period can be as short as 1 day with some antibiotics
Infections (bacterial, viral, parasitic) (5-10%)
Systemic disease (10-20%) • Autoimmune diseases (Sarcoidosis SLE, Sjögren’s, ANCA) • Neoplastic (leukemias, lymphomas) • Acute allograft rejection
Idiopathic (5-10%)
Acute Tubulointerstitial Nephritis
Causes of ATIN
Drug Induced
Common drugs associated with ATIN: antibiotics (particularly β-lactams, sulfas), NSAIDS including cyclooxygenase-2 (COX-2) inhibitors, proton pump inhibitors, diuretics, etc.
NSAIDS (and COX-2 inhibitors): These agents may induce kidney injury via various mechanisms:
Acute tubular necrosis due to acute afferent arteriolar vasoconstriction and resultant reduction in intraglomerular filtration pressure
Interstitial nephritis which may present as acute, chronic, or granulomatous interstitial nephritis.
Papillary necrosis in patients with underlying ischemic renal disease (e.g., patients with diabetes mellitus and associated arteriosclerosis, sickle cell disease)
Three-fourth of NSAIDS-induced ATIN is associated with nephrotic syndrome and glomerular lesions including minimal change disease, membranous glomerulonephropathy, and less commonly, focal segmental glomerulosclerosis (FSGS), membranoproliferative glomerulonephropathy. Risks include older age, chronic use, and use of fenoprofen.
Rifampin: Renal injury pattern may reflect pattern of use:
Intermittent or interrupted use:
Acute tubular necrosis with or without associated interstitial infiltrations, intravascular hemolysis, or thrombocytopenia
Patient may present with flu-like symptoms within hours of drug ingestion.
Continuous use: interstitial nephritis, light chain proteinuria, or even rapidly progressive glomerulonephritis