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Acute interstitial nephritis (AIN) is one of the major causes of Acute kidney injury who mainly present with non-oliguria. It is imperative to have tissue diagnosis of AIN in order to decide on therapy in cases who are not showing self-recovery of renal function and prevent them from disease progression. This study focuses on the clinical presentations, causes of AIN, outcomes and prognostic indicators.
Medical records, demographic and histopathological details of all biopsy proven AIN between January 2013 and December 2022 was retrieved from hospital information system. AIN associated with systemic diseases (such as SLE, Sjogren’s syndrome, sarcoidosis, plasma cell dyscrasias, IGG4 disease) and allograft biopsies were excluded. Cases with incomplete data were excluded.
Out of 6834 biopsies screened,170 (2.5%) biopsies showed features suggestive of AIN. Mean age of the cohort is 53.74 ± 16.4 years which is comprised of 129 males (75.9%). 44 patients (25.9%) had diabetes while 67 patients (39.4 %) were hypertensives. Nausea and vomiting (78.2%), pedal edema (58.8%) followed by oliguria (55.9%) were the most common symptoms. Drugs (74.7%), Infection causing AIN (14.1%), crystal associated AIN (5.8%), unknown cause (4.1%) and snake bite (1.2%) were among the etiology of AIN. Among drugs, NSAIDS (n=53; 31.2%), alternate form of medications (n=38; 22.4%) and antibiotics and proton pump inhibitors (n=20; 11.8%) were the most common causes of AIN. Bacterial infections (n=12; 7.1%) followed by viral infection (n=7;4.1%) including HIV (n=4) were among the culprits from infectious category. Among crystal associated AIN, calcium oxalate crystals (n=4), calcium phosphate crystals (n=4) and DHA crystals (n=2) were seen in the biopsy along with interstitial inflammation. Steroid was given to 121 patients (71.2%) of whom 98 patients (80.9%) showed renal recovery while 30 patients (17.6%) showed self renal recovery without steroid therapy (n=49 ;28.8%). Mean eGFR in steroid therapy group and in steroid naïve group at admission was 12.3 ± 11.2 vs 8.1 ± 5.1 ml/min/1.73m2 (p=0.34), at 3 months was 35.7 ± 25.7 vs 20.4 ± 16.8 (p=0.014) and at last follow up 48.3 ± 30.3 vs 26.5 ± 24.4 ml/min/1.73m2. Hemoglobin level >10gm/dl at presentation and steroid therapy for AIN (irrespective of the dose) were associated with renal recovery (p value= 0.02;0,005) respectively. In total, 34 patients (28.5%) succumbed to infections in steroid group vs 6 patients (11.9 %) in steroid naïve group (p=0.02).
Despite drug being the most common etiology of AIN, it showed good renal response to steroid therapy at the end of 3 months of follow up. Hemoglobin more than 10gm/dl and steroid therapy irrespective of the dose were associated with renal recovery in biopsy proven AIN patients. In view of substantial biopsy proven AIN patients, steroid therapy in non-recovery of AIN despite removing offending agent is being encouraged for renal recovery with caution.