Abstract
RATIONALE: Acute tubulointerstitial nephritis (ATIN) in children is most commonly due to allergic drug reactions. In neonates, diagnosis of ATIN is clinically suspected and a kidney biopsy is not routinely performed. PRESENTING CONCERN: A 17-day-old newborn presented with vomiting and dehydration, along with anuric acute kidney injury, severe electrolyte disturbances, hypocomplementemia, and thrombocytopenia. Abdominal ultrasound revealed bilateral nephromegaly and hepatosplenomegaly. The patient was promptly started on intravenous (IV) fluid and broad-spectrum antibiotics. His electrolyte disturbances were corrected as per standard guidelines. The rapid progressive clinical deterioration despite maximal treatment and the unclear etiology influenced the decision to proceed to a kidney biopsy. Histopathological findings revealed diffuse interstitial edema with a massive polymorphic cellular infiltrate and destruction of tubular structures, consistent with severe ATIN. Elements of thrombotic microangiopathy (TMA) were observed. DIAGNOSIS: The clinical presentation combined with imaging and histopathological findings was suggestive of ATIN caused by a severe acute bacterial pyelonephritis. INTERVENTION: Methylprednisolone pulses followed by oral prednisolone were administered. Antibiotics were continued for 10 days. The patient was kept on invasive mechanical ventilation and on peritoneal dialysis for 12 days. OUTCOME: His condition stabilized following steroid pulses. His renal function progressively improved, and renal replacement therapy was weaned off. His renal ultrasound normalized. He has maintained a normal blood pressure, urinalysis, and renal function over the past 5 years. NOVEL FINDING: This case reports a severe presentation of acute bacterial pyelonephritis in a neonate. It highlighted the involvement of complement activation in severe infectious process. Histopathological findings of ATIN and TMA played a crucial role in understanding the physiopathology and severity of the disease.