Overview
Acute interstitial nephritis (AIN) describes inflammation of the kidney interstitium usually triggered by a hypersensitivity reaction to drugs. It classically presents with a triad of rash, fever, and eosinophilia, however, this occurs rarely.
Causes
Drugs
Drugs are the most common cause of AIN and include:
- Nearly all penicillins and cephalosporins
- NSAIDs
- Rifampicin
- Proton pump inhibitors
- Allopurinol
Other causes
Other causes include:
- Infections (e.g. HIV and Epstein-Barr virus (EBV))
- Systemic autoimmune diseases (e.g. systemic lupus erythematosus (SLE) and Sjögren’s syndrome)
- Idiopathic
Presentation
Patients classically have a reduction in kidney function without oliguria within days of starting a causative drug. Other features include:
- The classic triad of AIN – rarely appears as all three (<10% of cases):
- Rash
- Fever
- Eosinophilia
- Elevated serum immunoglobulin E (IgE)
Differential Diagnoses
Acute tubular necrosis (ATN)
- Eosinophilia, rash, and elevated IgE make ATN less likely
- Urinalysis may show muddy brown casts in ATN
Investigations
- Urea and electrolytes (U&Es):
- Urea and creatinine are elevated
- Urinalysis:
- May show sterile pyuria – white cells in the urine with a negative bacterial culture
- Mild-moderate proteinuria may be seen
- Full blood count (FBC) and white cell differential:
- May show eosinophilia
- Trial of discontinuing suspected causative medication:
- Acute kidney injury (AKI) resolves
- Kidney biopsy – only test that gives a definitive diagnosis:
- Generally performed if AKI does not improve when withdrawing a causative medication, where the diagnosis is unclear, or if treatment involving immunosuppressants (e.g. corticosteroids) is being considered
- May show inflammatory infiltrates in the interstitium with varying numbers of eosinophils, lymphocytes and plasma cells
Management
Management involves:
- Withdrawal of the offending drug
- Supportive care (e.g. correcting derangements in U&Es and fluid balance)
- Corticosteroids may be considered in some cases
Complications
The main complication is the development of chronic kidney disease (CKD).
Prognosis
- Most patients with drug-induced AIN have some degree of impaired kidney function
- The prognosis is worse with delayed diagnosis and/or management