The effect of levodopa on speech graphs in non-demented patients with multiple system atrophy and Parkinson’s disease

Background An objective topological analysis for any arbitrary network was provided by graph theory, which was implemented to reveal topological properties of brain networks in a wide range of neurodegenerative diseases. Objectives To investigate the difference of the topology of speech graphs among parkinsonian-type multiple system atrophy patients (MSA-P), idiopathic Parkinson’s disease (PD) patients, and healthy controls (HC). To explore the effect of levodopa on the topology of speech graphs in MSA-P and PD patients. Methods We applied a graph analysis of topology of speech graphs in MSA-P patients ( N = 39), idiopathic PD patients ( N = 51), and HC ( N = 51). All participants were assessed by a well-established semantic fluency test (animal). Participants’ verbal reactions were listed and represented as speech graphs with directionality. Results MSA-P patients mentioned more about their memory and remaining time than PD patients ( p < 0.001) and HC ( p < 0.001). Moreover, MSA-P patients’ speech graphs exhibited fewer nodes (PD: p = 0.004; HC: p < 0.001), higher density (PD: p = 0.007; HC: p < 0.001), smaller diameter (PD: p = 0.004; HC: p < 0.001), and smaller average shortest path (PD: p = 0.002; HC: p < 0.001) than both PD patients and HC. Compared with PD patients and healthy adults, the MSA-P patients generated denser and smaller speech graphs. Importantly, in MSA-P, the positive correlations between levodopa equivalent daily dose and diameter ( r = 0.39, p = 0.017) and average shortest path ( r = 0.38, p = 0.017) were obtained, suggesting that higher levodopa doses were associated with producing sparser and larger speech graphs in MSA-P patients. However, there was no significant correlation between levodopa equivalent daily dose and graph indices in PD patients. Conclusion MSA-P patients’ speech graphs were denser and smaller than both PD patients and healthy adults. The graph analysis of semantic fluency can differentiate MSA-P from PD to some extent. Importantly, in MSA-P patients, the impaired speech topology can be partially restored by levodopa.