The Impact of Nonmotor Symptoms on Health-Related Quality of Life in Parkinson's Disease: A Network Analysis Approach

Abstract

Nonmotor symptoms negatively affect health-related quality of life (HRQoL) in patients with Parkinson's disease (PD). However, it is unknown which nonmotor symptoms are most commonly associated with HRQoL. Considering the complex interacting network of various nonmotor symptoms and HRQoL, this study aimed to reveal the network structure, explained HRQoL variance, and identify the nonmotor symptoms that primarily affect HRQoL. We included 689 patients with PD from the Cohort of Patients with Parkinson's Disease in Spain (COPPADIS) study who were rated on the Nonmotor Symptoms Scale in Parkinson's disease (NMSS) and the Parkinson´s Disease Questionnaire 39 (PDQ-39) at baseline. Network analyses were performed for the 30 items of the NMSS and both the PDQ-39 summary index and eight subscales. The nodewise predictability, edge weights, strength centrality, and bridge strength were determined. In PD, nonmotor symptoms are closely associated with the mobility, emotional well-being, cognition, and bodily discomfort subscales of the PDQ-39. The most influential nonmotor symptoms were found to be fatigue, feeling sad, hyperhidrosis, impaired concentration, and daytime sleepiness. Further research is needed to confirm whether influencing these non-motor symptoms can improve HRQoL.

Keywords: NMSS; PDQ-39; Parkinson disease; cognition; depression; disorders of excessive somnolence; fatigue; hyperhidrosis; network analysis; nonmotor symptoms; quality of life.

Figure 1

Network structure of the Nonmotor Symptoms Scale in Parkinson’s disease (NMSS) and Parkinson’s Disease Questionnaire 39 (PDQ-39) summary index. The node PDQ displays the PDQ-39 summary index, and nodes i1–i30 display the items included in the NMSS. The thickness of the edges indicates the strength of the correlations between these nodes. Color coding represents the assignment of the items to the nine domains of the NMSS: cardiovascular (domain 1; items 1 and 2); sleep/fatigue (domain 2; items 3, 4, 5, and 6); mood/cognition (domain 3; items 7, 8, 9, 10, 11, and 12); perceptual problems (domain 4; items 13, 14, and 15); attention/memory (domain 5; items 16, 17, and 18); gastrointestinal tract (domain 6; items 19, 20, and 21); urinary (domain 7; items 22, 23, and 24); sexual function (domain 8; items 25 and 26); and miscellaneous (domain 9; items 27, 28, 29, and 30). Item 1: light headedness; item 2: fainting; item 3: daytime sleepiness; item 4: fatigue; item 5: sleep initiation; item 6: restless legs; item 7: loss of interest; item 8: lack of motivation; item 9: feeling nervous; item 10: feeling sad; item 11: flat mood; item 12: anhedonia; item 13: hallucinations; item 14: delusions; item 15: diplopia; item 16: concentration; item 17: forgetfulness; item 18: forget to do things; item 19: sialorrhea; item 20: dysphagia; item 21: constipation; item 22: urgency; item 23: frequency; item 24: nocturia; item 25: interest; item 26: problems having sex; item 27: pain; item 28: taste/smell; item 29: weight change; and item 30: hyperhidrosis.

Figure 2

Node strength of the NMSS and PDQ-39 summary index. The strength centrality measures of PDQ-39 summary index (PDQ) and the items of the NMSS (i1–i30) are given in standardized values. Item 1: light headedness; item 2: fainting; item 3: daytime sleepiness; item 4: fatigue; item 5: sleep initiation; item 6: restless legs; item 7: loss of interest; item 8: lack of motivation; item 9: feeling nervous; item 10: feeling sad; item 11: flat mood; item 12: anhedonia; item 13: hallucinations; item 14: delusions; item 15: diplopia; item 16: concentration; item 17: forgetfulness; item 18: forget to do things; item 19: sialorrhea; item 20: dysphagia; item 21: constipation; item 22: urgency; item 23: frequency; item 24: nocturia; item 25: interest; item 26: problems having sex; item 27: pain; item 28: taste/smell; item 29: weight change; and item 30: hyperhidrosis. NMSS: Nonmotor Symptoms Scale in Parkinson´s disease. PDQ-39: Parkinson´s Disease Questionnaire 39.

Figure 3

Network structure of the NMSS and PDQ-39 subscales. The blue nodes display the PDQ-39 subscales (MOB, ADL, EMO, STI, SOC, COG, COM, and BOD), and the orange nodes display the items included in the NMSS (i1–i30). The thickness of the edges indicates the strength of the correlations between these nodes. Item 1: light headedness; item 2: fainting; item 3: daytime sleepiness; item 4: fatigue; item 5: sleep initiation; item 6: restless legs; item 7: loss of interest; item 8: lack of motivation; item 9: feeling nervous; item 10: feeling sad; item 11: flat mood; item 12: anhedonia; item 13: hallucinations; item 14: delusions; item 15: diplopia; item 16: concentration; item 17: forgetfulness; item 18: forget to do things; item 19: sialorrhea; item 20: dysphagia; item 21: constipation; item 22: urgency; item 23: frequency; item 24: nocturia; item 25: interest; item 26: problems having sex; item 27: pain; item 28: taste/smell; item 29: weight change; and item 30: hyperhidrosis. PDQ-39 subscale coding: MOB, mobility; ADL, activities of daily living; EMO, emotional well-being; STI, stigma; SOC, social support; COG, cognition; COM, communication; BOD, bodily discomfort. NMSS: Nonmotor Symptoms Scale in Parkinson´s disease. PDQ-39: Parkinson´s Disease Questionnaire 39.

Figure 4

Bridge strengths of the NMSS and PDQ-39 subscales. The bridge strength indicates the sum of the values of all edges that exist between a node of one community and all nodes from another community. Bridge strength values are given for the nodes of the NMSS (i1–i30) and PDQ-39 subscales (MOB, ADL, EMO, STI, SOC, COG, COM, and BOD). Item 1: light headedness; item 2: fainting; item 3: daytime sleepiness; item 4: fatigue; item 5: sleep initiation; item 6: restless legs; item 7: loss of interest; item 8: lack of motivation; item 9: feeling nervous; item 10: feeling sad; item 11: flat mood; item 12: anhedonia; item 13: hallucinations; item 14: delusions; item 15: diplopia; item 16: concentration; item 17: forgetfulness; item 18: forget to do things; item 19: sialorrhea; item 20: dysphagia; item 21: constipation; item 22: urgency; item 23: frequency; item 24: nocturia; item 25: interest; item 26: problems having sex; item 27: pain; item 28: taste/smell; item 29: weight change; and item 30: hyperhidrosis. PDQ-39 subscale coding: MOB, mobility; ADL, activities of daily living; EMO, emotional well-being; STI, stigma; SOC, social support; COG, cognition; COM, communication; BOD, bodily discomfort. NMSS: Nonmotor Symptoms Scale in Parkinson´s disease. PDQ-39: Parkinson´s Disease Questionnaire 39.