A 45-year old male with left-sided hemihypesthesia

A 45-year-old man presented with progressive brainstem and cerebellar dysfunction. Extensive immunological and radiological investigations were not able to differentiate between an intrinsic brain tumor and a demyelinating disease. Stereotactic biopsies of the brainstem were performed; the findings of abundant Rosenthal fibers, interjacent spindle-shaped and gemistocytic cells partially with dark and irregularly formed nuclei favored primarily the diagnosis of a malignant astrocytoma, although a demyelinating disease could not be definitely excluded. Facing the fulminant clinical course radio- and chemotherapy was initiated; however, the patient died of sepsis-associated multi-organ failure three and a half years after disease onset. Post mortem pathology finally revealed lesions with central amorphic necrosis surrounded by areas of significant demyelination, astrocytosis, microglia cells and macrophages typical for MS. Although criteria for establishing MS are well known, a correct diagnosis can be extremely challenging in small stereotactic specimens, where so-called pathological hallmarks are spared and unusual pathological findings are predominant.