Forms of Chronic Interstitial Nephritis Associated with Hypertension
Several forms of chronic interstitial nephritis (CIN) can cause or are associated with hypertension, with nephrosclerosis and analgesic nephropathy being the most common culprits.
Primary Forms of CIN Associated with Hypertension
1. Nephrosclerosis
- Nephrosclerosis is a significant cause of chronic interstitial nephritis that is directly associated with hypertension 1
- Characterized by vascular changes in the kidney, including medial hypertrophy and abnormal extension of muscle to peripheral arteries
- Creates a bidirectional relationship where hypertension both causes and is worsened by the kidney damage
2. Analgesic Nephropathy
- Results from long-term intake of NSAIDs and compound analgesics 2, 3
- Features chronic interstitial nephritis with capillary sclerosis and papillary necrosis
- Hypertension develops as kidney function deteriorates
- Even young patients can develop this condition with prolonged NSAID use 2
3. Tuberous Sclerosis Complex (TSC)
- Patients with TSC have a higher risk of developing hypertension
- Risk increases with advanced CKD, high angiomyolipoma stage, or history of embolization procedures 4
- Blood pressure monitoring is essential in these patients, with targets following CKD guidelines
4. Agricultural Chemical Exposure (CINAC)
- Chronic interstitial nephritis in agricultural communities (CINAC) is associated with exposure to nephrotoxic agrochemicals 5
- Characterized by tubular injury, tubulointerstitial inflammation, and fibrosis
- Hypertension can develop as the disease progresses
Secondary Causes and Contributing Factors
1. Renal Artery Stenosis
- A common cause of resistant hypertension, particularly in older patients 4
- Can coexist with chronic interstitial nephritis, worsening both conditions
- 35% of secondary causes of resistant hypertension are associated with occlusive renovascular disease 4
2. Chronic Kidney Disease Progression
- As CIN progresses to chronic kidney disease (CKD), hypertension becomes more prevalent
- 30.2% of patients with stage 1 CKD have hypertension, increasing to 78.9% with stage 4 CKD 4
- Resistant hypertension is more common with lower eGFR, with 54.2% of patients with eGFR <30 mL/min/1.73m² having apparent treatment-resistant hypertension 4
Management Considerations
Blood Pressure Targets
- For patients with CKD and hypertension, the BP goal should be less than 130/80 mm Hg 4
- In patients with proteinuria >1g/day, a more aggressive target of <125/75 mm Hg is recommended 4
Medication Selection
- ACE inhibitors or ARBs are recommended as first-line agents for patients with CKD stage 3 or higher or with significant albuminuria 4
- These medications should be used cautiously in patients with bilateral renal artery stenosis, as they can cause acute kidney injury 6
- Calcium channel blockers have been proposed as first-line agents in some cases due to their ability to block CNI-induced vasoconstriction 4
Monitoring and Follow-up
- Regular monitoring of kidney function is essential, particularly in high-risk patients
- Temporary reduction or discontinuation of ACE inhibitors/ARBs may be necessary during acute illness or before contrast procedures 6
- The combination of ACE inhibitors/ARBs, diuretics, and NSAIDs significantly increases the risk of acute kidney injury 6
Prevention Strategies
- Avoid nephrotoxic medications when possible, particularly NSAIDs in patients with existing kidney disease
- Reduce salt intake to <2 grams of sodium per day to improve blood pressure control and slow CKD progression 4
- Monitor for early signs of kidney dysfunction, including decreased urine output, edema, and rising creatinine levels
- Consider temporary discontinuation of ACE inhibitors/ARBs during periods of dehydration or before procedures with contrast agents
By identifying the specific form of chronic interstitial nephritis and addressing both the underlying cause and hypertension, progression of kidney disease can be slowed and cardiovascular risk reduced.