Electroglottography (EGG) is a noninvasive technique which allows accurate measurements of vocal folds dynamics and perturbations during speech. It has been widely used in medical diagnosis and monitoring of several laryngeal pathologies, but its use in neurological disorders has been very limited. This paper presents the first study on EGG in early stages of Parkinson's disease (PD) and an atypical parkinsonian disorder, multiple system atrophy (MSA). Our first objective was to investigate whether EGG can reveal distinctive dysphonia features that could help in the challenging early differential diagnosis between PD and MSA-P, the parkinsonian variant of MSA. The second objective was to verify some hypothesis on early markers of PD drawn from speech-alone acoustic analysis. For MSA-P patients, our analysis revealed a reduced open quotient and confirmed excessive pitch variation. The analysis also mitigated some hypothesis on dysphonia in early stages of PD.