Comorbidity of mitochondrial disease and dementia in patients with idiopathic polyneuropathy

Background and purpose Studying the comorbidities of chronic idiopathic axonal polyneuropathy (CIAP) might help to better understand its etiopathogenesis. We aimed to assess the associations of mitochondrial disease (MD), Alzheimer's disease (AD) and vascular dementia (VD) with CIAP. Methods In this nested case‐control study we included 2659 patients with CIAP identified from the Swedish Patient Register and 13 295 age‐ and sex‐matched controls to assess the associations of MD, AD and VD with the subsequent risk of CIAP. We also conducted a follow‐up study of the cases and controls to assess the risk of MD, AD or VD among patients with CIAP in comparison to individuals without CIAP. Results Individuals with MD had an increased risk of subsequent CIAP [odds ratio (OR), 4.17; 95% confidence intervals (CI), 1.27–13.65], whereas individuals with AD and VD had a decreased risk (OR, 0.18; 95% CI, 0.06–0.59 and OR, 0.17; 95% CI, 0.04–0.69). Patients with CIAP had a ninefold increased risk of subsequent MD [hazard ratio (HR), 9.37; 95% CI, 4.00–21.93], twofold increased risk of VD (HR, 1.97; 95% CI, 1.23–3.16), but no increased risk of AD (HR, 1.33; 95% CI, 0.89–1.98) compared with individuals without CIAP. Conclusions We found a higher risk of MD among patients with CIAP, both before and after the diagnosis of CIAP. We found a higher risk of VD, but not AD, after the diagnosis of CIAP. The lower risks of AD and VD before CIAP might be due to a reduced surveillance of CIAP symptoms among patients with dementia.