We describe a 13-years-old girl, previously diagnosed with PTPN11-associated Noonan Syndrome (NS), who presented to the pediatric emergency department for fever and drowsiness, which gradually worsened within 48 h. On admission, brain magnetic resonance imaging (MRI) scan showed diffuse, symmetric, multiple, poorly demarcated, confluent hyperintense lesions on MRI T2w-images, located in the Central Nervous System (CNS). In the absence of a better explanation and according to the current diagnostic criteria, a diagnosis of Acute Disseminated Encephalomyelitis (ADEM) was performed. The patient was first treated with intravenous methylprednisolone, then with intravenous immunoglobulin (IVIG). Owing to the poor clinical response, three sessions of therapeutic plasma exchange (TPE) were finally performed, with a progressive improvement. Follow-up MRI performed after three months from the onset revealed a considerable reduction in brain lesions, while cervical and dorsal ones were substantially unmodified. Neurological examination showed a full recovery of cognitive function and improved strength and tone of the upper limbs, while tetrahyporeflexia and proximal weakness of lower limbs were still appreciable. To date, this is the first described case of ADEM occurring in a patient with NS.
