Recurrent acute focal bacterial nephritis presenting with meningitis-like symptoms and discordant occurrence of MERS in a late-adolescent male

Mild encephalitis/encephalopathy with a reversible splenial lesion (MERS) is usually reported in children with viral infections; bacterial triggers such as acute focal bacterial nephritis (AFBN) are uncommon. We describe a physically mature 16-year-old male with two episodes of AFBN presenting with high fever, severe headache and meningeal signs but essentially normal cerebrospinal fluid (CSF) findings. During the first episode, brain magnetic resonance imaging (MRI) showed a type 1 splenial lesion consistent with MERS, and contrast-enhanced abdominal computed tomography (CT) demonstrated right-sided AFBN. Serum and CSF interleukin-6 (IL-6) were markedly elevated with mild hyponatremia. Symptoms resolved and the splenial lesion disappeared after intravenous ceftriaxone followed by oral antibiotics. Six weeks later, the patient developed recurrent AFBN in the same renal region with a similar clinical presentation and comparable elevations of serum and CSF IL-6; however, repeat brain MRI showed no splenial or other callosal lesions. He recovered fully after a prolonged six-week course of oral antibiotics. This two-episode observation expands the demographic spectrum of AFBN-associated MERS and suggests that IL-6 elevation alone may not be sufficient to induce a splenial lesion; additional transient susceptibility of the splenium and/or osmotic factors may be required.