Send to

Choose Destination
J Neurol Sci. 2015 Feb 15;349(1-2):226-8. doi: 10.1016/j.jns.2014.12.019. Epub 2014 Dec 18.

Clinically mild encephalitis with a reversible splenial lesion (MERS) after mumps vaccination.

Author information

Department of Pediatrics, Tokyo Women's Medical University, Yachiyo Medical Center, Yachiyo, Japan. Electronic address:
Department of Neurology, Gunma Children's Medical Center, Shibukawa, Japan.
Department of Pediatrics, Soka Municipal Hospital, Soka, Japan.
Division of Pediatrics, Sendai City Hospital, Sendai, Japan.
Department of Pediatrics & Child Health, Kurume University School of Medicine, Kurume, Japan.
Department of Pediatrics, Aichi Medical University, Nagakute, Japan.
Department of Developmental Medical Sciences, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan.


We retrospectively collected three patients with clinically mild encephalitis with a reversible splenial lesion (MERS) after mumps vaccination, and reviewed five patients, including two patients previously reported. The five patients (all males, aged 1 to 9) presented with fever, vomiting, or headache as the initial symptoms (day 0), suggesting meningitis, at 13 to 21 days after mumps vaccination. Consciousness disturbance, delirious behavior, seizures, or dysarthria was observed on days 1 to 3, which had completely resolved before day 11. Hyponatremia was observed in all patients. A cerebrospinal fluid study showed pleocytosis, and confirmed the vaccine strain genome. MRI revealed reduced diffusion in the splenium of the corpus callosum on days 2 to 4, which had completely disappeared on the follow-up studies performed on days 7-15. EEG showed high voltage slow wave in three patients, which later normalized. These findings led to a diagnosis of MERS after mumps vaccination. MERS after mumps vaccination may be more common than previously considered. MERS is suspected when a male patient after mumps vaccination presents with neurological symptoms with hyponatremia, following symptoms of aseptic meningitis, and MRI would be performed to examine the splenium of the corpus callosum.


Clinically mild encephalitis/encephalopathy with a reversible splenial lesion (MERS); Diffusion; Hyponatremia; MRI; Mumps vaccination; Splenium

[Indexed for MEDLINE]

Supplemental Content

Full text links

Icon for Elsevier Science
Loading ...
Support Center