Posterior fossa syndrome with a large inflammatory ponto-mesencephalic lesion

•The patient clinically presented with a cerebellar and dysexecutive syndrome.•He had a clinically isolated syndrome with a single ponto-mesencephalic lesion.•The probable explanation of his symptoms is a pontine disconnection syndrome.•It is the first posterior fossa syndrome due to a pontine disconnection syndrome.

Demonstration of a posterior fossa syndrome (PFS) in a 32-year-old male patient with clinically isolated syndrome which subsequently developed into relapsing-remitting Multiple Sclerosis.The patient suffered from double vision, coordination problems including unsteady gait and atactic dysarthria, concentration difficulties, as well as adynamia and impaired decision making.The patient clinically presented a cerebellar and dysexecutive syndrome. Cerebral magnetic resonance imaging (MRI) revealed a contrast enhancing ponto-mesencephalic lesion with a volume of 4.8 cm3. Neuropsychological tests showed pronounced executive dysfunctions, reduced visuoconstructive skills, attentional deficits, echolalia, and non-fluent speech production.After cortisone and plasmapheresis, the cerebellar syndrome improved but manual fine motor skills and executive dysfunctions persisted.After three months, symptoms remitted except for a slight gait imbalance. After six months, neuropsychological tests were normal except for a moderate attention deficit. MRI revealed a clear regression of the ponto-mesencephalic lesion to a volume of 2.4 cm3 without contrast enhancement.This case report intends to provide an overview of the symptomatology and etiology of PFS and offers new insights into its pathomechanism demonstrating a pontine disconnection syndrome caused by a large demyelinating plaque.