Aim: Encephalitis lethargica spread as a pandemic over the period 1918-1921. Clinically, it displayed an important degree of polymorphism and the clinical presentation varied from one outbreak to the next and from one region to another. Few studies have been carried out on the encephalitis lethargica epidemic in Spain. To determine the characteristics of its clinical and developmental features, we reviewed the cases reported in the Spanish medical literature over the period 1918-1936.
Development: A total of 120 cases were analysed. Most of them (75%) occurred during the winter of 1919-1920. The mean age was 27 years (range: 0-59 years). Most of them presented feverish syndromes (82%). The most frequent neurological symptoms were disorders affecting the cranial nerves, especially the oculomotor nerves, sleep rhythm disorders, altered mental or conscious status, pupillary abnormalities and movement disorders. Important variations were observed in the clinical presentation and in the developmental course. Although most cases did not present pure clinical forms, the predominant forms were somnolent-ophthalmoplegic (46%) and hyperkinetic (17%), which were associated with delusions with chorea or myoclonias. The most uncommon were amyostatic forms (Parkinsonian, 4%). The mortality rate was 23%. Most of the survivors (69%) were cured in the acute phase with no significant sequelae.
Conclusions: The maximum incidence of encephalitis lethargica in Spain was registered during the winter of 1919-1920. It presented an important degree of clinical polymorphism, with predominance of an association between lethargy and ophthalmoplegia, and was linked to a high mortality rate.