Objective monitoring of motor symptom severity and their progression in Parkinson’s disease using a digital gait device by Raschka, Tamara, To, Jackrite, Hähnel, Tom, Sapienza, Stefano, Ibrahim, Alzhraa, Glaab, Enrico, Gaßner, Heiko, Steidl, Ralph, Winkler, Jürgen, Corvol, Jean-Christophe, Klucken, Jochen, Fröhlich, Holger