[An acute meningo-encephalitis with a favourable prognosis and occasional severe electrical and clinical changes; infectious mononucleosis meningo-encephalitis (author's transl)].

Four cases of severe meningo-encephalitis in patients with infectious mononucleosis (IMN) are reported. In three cases the clinical context suggested a mononucleosis. In the other case there was fever but only isolated neurological signs, which demonstrates the importance of serological diagnostic tests because of the benign prognosis of this affection. In fact, neurological complications of IMN are considered to be reversible even though deaths have occurred from respiratory failure, from polyradiculoneuritis, or bulbar involvement. In the cases reported, the onset of a deep coma with loss of reflexes and pauses in respiration required resuscitation therapy, which enabled vital functions to be restored and complete recovery to be obtained. Electro-encephalographic changes were marked by the severity of the initial changes in the tracings with very slow delta waves and prolonged electrical silences which were, however, reversible. The prognostic value of the EEG has to be stressed as improvement in the EEG always preceded clinical improvement.