Compliance with ethical standards: the study was approved by the Ivanovo State Medical Academy ethics committee and is a part of the earlier research (protocol № 5 of June 03, 2009). All patients signed a voluntary informed consent to participate in the study.

Author contribution: Pochernikov DG — research planning, literature analysis, data interpretation and analysis, manuscript drafting, preparation of the final version of the article; Postovoytenko NT — literature analysis, data collection, analysis and interpretation, manuscript drafting, preparation of the final version of the article; Getman VV — data collection, analysis and interpretation, manuscript drafting; Galkin IS — research planning, data interpretation, manuscript drafting, preparation of the final version of the article.