The impact of COPD on polyneuropathy: results from the German COPD cohort COSYCONET

Background: Peripheral neuropathy is a common comorbidity in COPD, for which various associations with COPD characteristics have been reported. We aimed to identify effects of changes associated with COPD on neuropathy, distinguishing between direct and indirect associations.

Methods: We used visit 4 data of the COPD cohort COSYCONET, which included indicators of polyneuropathy (repeated tuning fork, monofilament testing), excluding patients with diabetes a/o increased HbA1c. These indicators were analysed for the association with COPD characteristics, including lung function, blood gases, 6-minute walk distance (6-MWD), the timed-up-and-go-test (TUG), exacerbation risk according to GOLD, C-reactive protein (CRP), and ankle-brachial index (ABI). Based on the results of conventional regression analyses adjusted for age, BMI, packyears and gender, we utilized structural equation modelling (SEM) to quantify the network of direct and indirect relationships between parameters.

Results: 606 patients were eligible for analysis. The indices of polyneuropathy were highly correlated with each other and related to base excess (BE), ABI and TUG. ABI depended on neuropathy and 6-MWD, exacerbations depended on FEV1, 6-MWD and CRP. The associations could be summarized into a SEM comprising polyneuropathy as a latent variable (PNP) with three measured indicator variables. Importantly, PNP was directly dependent on BE and ABI. When also including patients with diabetes and/or elevated values of HbA1c (n = 742) the SEM remained virtually the same.

Conclusion: We identified BE and ABI as major determinants of peripheral neuropathy in patients with COPD. All other associations, particularly those with lung function and physical capacity, were indirect. These findings underline the importance of alterations of the micromilieu associated with COPD, in particular vascular status and the degree of metabolic compensation.