[Clinical pathogenic peculiarities of chronic Russian tick-born encephalitis].

Clinical, serologic, epidemiological and neurological studies were carried out in 23 patients (18 men, 5 women) aged 15-69 years who had chronic Russian tick-borne encephalitis (RTE). With permanent stable humoral immunity the fact that these forms might develop was confirmed in 73.9% of the cases. In 26.1% of the patients were found to have incomplete vaccination and vaccine therapy combined with RTE viral infection. The following conditions underlay chronization were observed in all forms of acute RTE: fever in 4.3%, meningitis in 30.4%, focal lesion in 43.5% (the encephalitic syndrome in 8.7%, poliomyelitis in 8.7%, encephalopoliomyelitis in 26.1%). Initially progressive course was found in 21.7% of the cases. There was a primary rise of the hyperkinetic syndrome after the meningeal and focal forms of RTE with the encephalitic syndrome; while development of the amyotrophic syndrome (ATS) was found after the focal form with the poliomyelitic and encephalopoliomyelitic syndrome. The amyotrophic lateral sclerosis (ALS) syndrome occurs as both primary progressive RTE and ATS transformation independently of the initial RTE form. Latent periods of development of ATS and ALS syndrome were virtually equal (mean 1.4 years) and did not depend on the initial form of acute RTE. The duration of development of latent chronic forms makes it necessary to follow up RTE patients for at least 3 years.