[Benign encephalitis of the brain stem].
INTRODUCTION: The secondary encephalitis disorders are due to an immunological mechanism which causes demyelinating lesions of the central and peripheral nervous systems, with very variable clinical features. The pathogenesis and localization of benign encephalitis of the brain stem and the Miller Fisher syndrome (MFS) are still subject to debate. It is suggested that they may both belong to different extremes of the same nosological spectrum known as the ophthalmoplegia-ataxia-areflexia syndrome. CLINICAL CASE: We report the case of an 11 year old boy with encephalitis of the brain stem who had electromyographic alterations compatible with the Guillain-Barré syndrome, and MR images characteristic of an acute demyelinating disorder of the brainstem. CONCLUSIONS: The encephalitis of the brain stem is an uncommon condition in children which leads to diagnostic difficulty at its onset, since this is similar in other disorders such as MFS, tumours, cerebrovascular accidents and less often in the initial stages of multiple sclerosis. The clinical course is very useful to distinguish between these conditions. MR is the imaging technique of choice for diagnosis in these patients. Although there is currently no specific treatment for post-infectious encephalitis, the use of high doses of immunoglobulins may be justified in view of the physiopathological origin of the condition.