Pathologic-MRI Findings in Atypical IIDD

Idiopathic inflammatory demyelinating disorders (IIDD) are a group of diseases with distinct clinical and magnetic resonnance imaging (MRI) features, the most frequent being Multiple Sclerosis (MS). MS can present with atypical MRI features that can be misleading. Neuromyelitis Optica Spectrum Disorder (NMOSD) is the main differential diagnosis. It has been demonstrated that some patient with NMOSD can also present with brain lesion that is sometimes difficult to diagnose. In this context, a retrospective series identifies 18 patients with centreal nervous system atypical demyelination and 1) pathological evidence of astrocytopathy and 2) immunohistochemistry demonstrating decrease of aqp4 binding. The aim of the study is to describe the radiological and pathological characteristics of a series of patients with pathologicaly proven atypical demyelination that underwent biopsy for diagnostic uncertainties.

This is a retrospective multicenter study. Inclusion criteria are: 1) Acute or subacute onset of neurological deficit, 2) Brain biopsy performed for diagnostic uncertainties revealing an active demyelinating lesion, 3) no known diagnosis of MS or NMOSD at the time of the biopsy and 4) no alternative diagnosis identified during the disease course.

All the medical records of the patients will be reviewed and the following data will be recorded: previous medical history including previous neurologic relapses, gender, age at onset, clinical symptoms at onset and diagnosis at last follow-up according to current diagnosis criteria for MS and NMOSD.

Brain MRI scanners will be analysed. The investigators will mainly focus on T1-, T2-, T2 gradient echo-, fluid- attenuated inversion recovery- and diffusion-weighted images. The following data will be recorded: number of lesions, location (cortical, juxtacortical, juxtaventricular, corpus callosum involvement, posterior fossa involvement), presence of a peripheral hyperintense/hypointense rim (on T2 sequence), and type of gadolinium enhancement (peripheral open or closed ring, central homogeneous or heterogeneous). The presence of oedema will be recorded and mass effect will be analysed. According to the classification of atypical demyelinating lesions (MAGNIMS group), patients will be classified as having either infiltrative, megacystic, balo-like, ring-like lesions or unclassified. Three neuropathologists (BL, BL and VR) blinded to the MRI and clinical datas will perform all the pathologic evaluations. Paraffin-embedded sections have been stained using hematoxylin \& eosin, Luxol fast blue. Primary antibodies specific fot GFAP, CD3, CD8, CD20 and CD68 were used in routine practice. Additional immunohistochemical studies will be done using primary antiobodies specific for IgG and Aquaporin-4. The investigators will specifically look at the presence of 1) morphologic features suggestive of either MS (Creutzfeldt cells) or NMOSD (dystrophic astrocytes, myelin vacuolation, vascular hyalinization) 2) negative aquaporin-4 staining (suggestive of NMOSD) and 3) macrophages containing GFAP positive or Luxol fast blue positive debris.