Comparison of mild encephalopathy with reversible splenial lesion with and without acute focal bacterial nephritis.

Objective: Clinically mild encephalitis/encephalopathy with a reversible lesion (MERS) is characterized by reversible lesions with transiently-reduced diffusion in the splenium of the corpus callosum on magnetic resonance imaging. Recently, cases of MERS with accompanying acute focal bacterial nephritis (AFBN) have been reported in children. This study aimed to clarify the clinical features of MERS with AFBN.

Methods: A retrospective study of patients with MERS was conducted at Nagano Children's Hospital, Japan, from April 2013 to March 2018. The clinical signs and laboratory findings of MERS patients with AFBN (AFBN group) and without AFBN (non-AFBN group) were measured and compared.

Results: Of 12 patients diagnosed as having MERS, 3 were also found to have AFBN. Seven of the 9 patients without AFBN were associated with infectious agents, including rotavirus and influenza viruses. No patient received steroids or intravenous immunoglobulin therapy, and none displayed neurological sequelae. Serum C-reactive protein (CRP) levels were significantly higher in the AFBN group than in the non-AFBN group (14.7 mg/dL versus 0.8 mg/dL, P = 0.009). AFBN group patients were also significantly older (97 months versus 27 months, P = 0.018) and experienced significantly less frequent seizures (33% versus 100%, P = 0.045). The mean duration of neurological symptoms was significantly longer in the AFBN group than in the non-AFBN group (4 days versus 1.7 days, P = 0.013).

Conclusions: Pediatric patients with AFBN often present with non-specific findings, such as fever and abdominal pain. Pediatricians should be aware of the possibility of AFBN in the clinical setting of MERS, particularly when the patient exhibits inexplicably high CRP.