1. Patient Presentation
A 61-year-old man presented with an 11-day history of fever and altered behavior, including repeatedly calling the police and making incoherent statements. On admission, he was alert and oriented but agitated with inappropriate verbalizations. Physical examination revealed right costovertebral angle tenderness without meningeal signs. Neurologic examination was otherwise normal. Laboratory investigations showed elevated white blood cell count and C-reactive protein levels. Electrolyte abnormalities, uremia, and hyperammonemia were absent. Cerebrospinal fluid analysis demonstrated a normal cell count. Initial head computed tomography showed no acute abnormalities but revealed increased fat density around the right kidney. Brain magnetic resonance imaging (MRI) demonstrated hyperintense lesions in the splenium of the corpus callosum on both T2-weighted and diffusion-weighted sequences (Fig, A,B). Urine culture yielded Enterococcus faecalis.
Figure.
Brain MRI findings in MERS associated with acute pyelonephritis. (A), and (B), Initial brain MRI on hospital day 1 showing hyperintense lesions in the splenium of the corpus callosum on T2-weighted (A) and diffusion-weighted (B) images (arrowheads). (C) Follow-up T2-weighted brain MRI on hospital day 8 demonstrating complete resolution of the splenial lesions (arrowhead). MRI, magnetic resonance imaging.
The patient received antimicrobial therapy for acute pyelonephritis. By hospital day 3, abnormal behavior had resolved completely and inflammatory markers had normalized. Follow-up brain MRI on hospital day 8 showed complete resolution of the splenial lesions (Fig, C).
2. Diagnosis: Mild Encephalitis/Encephalopathy with a Reversible Splenial Lesion Associated with Enterococcusfaecalis Acute Pyelonephritis
The diagnosis of mild encephalitis/encephalopathy with a reversible splenial lesion (MERS) associated with Enterococcus faecalis acute pyelonephritis was made based on clinical and neuroimaging findings. MERS predominantly affects pediatric patients, with adult cases being rare.1 A 2024 review reported a mean age of 28.9 years for adult-onset MERS, making this patient notably older.2 Approximately 70% of adult cases lack identifiable triggers, and E. faecalis pyelonephritis has not been reported as a MERS trigger.2 This case emphasizes considering MERS in adults with altered behavior during systemic infection. The reversible splenial lesions distinguish MERS from other encephalitic processes.
Funding and Support
By JACEP Open policy, all authors are required to disclose any and all commercial, financial, and other relationships in any way related to the subject of this article as per ICMJE conflict of interest guidelines (see www.icmje.org). The authors have stated that no such relationships exist.
Conflict of Interest
All authors have affirmed they have no conflicts of interest to declare.
Footnotes
Supervising Editor: John Rogers, MD
References
- 1.Romeo M., Polselli M., Mantero V., Moavero R., Mazzone L., Valeriani M. Clinical variability of pediatric MERS: insights from a retrospective observational study. J Clin Med. 2025;14:4169. doi: 10.3390/jcm14124169. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 2.Yuan J., Yang S., Wang S., Qin W., Yang L., Hu W. Mild encephalitis/encephalopathy with reversible splenial lesion (MERS) in adults-a case report and literature review. BMC Neurol. 2017;17:103. doi: 10.1186/s12883-017-0875-5. [DOI] [PMC free article] [PubMed] [Google Scholar]