CSF analysis demonstrated a mild lymphocytosis with normal protein level.

Poliomyelitis-like syndrome (resulting in anterior horn syndrome) is an infective myelitis by pathogens which selectively involve the anterior horn cells to cause an acute flaccid paralysis.  

The archetypical infective agent is poliomyelitis, although due to high rates of vaccination it is now more common for outbreaks of enterovirus 71 or West Nile virus to be implicated.  Other picornaviruses and flaviviruses such as coxsackie A and B viruses, Japanese encephalitis virus and Murray Valley virus are rare causes of poliomyelitis-like syndrome, with encephalitic presentations far more common than anterior horn cell involvement.

The typical MRI appearance is long segment T2 hyperintensity centered on the anterior horns, usually non enhancing.

There may also be imaging findings related to concurrent encephalitis.  Bilateral thalamic and brainstem involvement is the classic distribution of findings in encephalitis due to flaviviruses such as Japanese encephalovirus and West Nile virus.