Cough reflex sensitivity and urge-to-cough deterioration in dementia with Lewy bodies

Cough, an important respiratory symptom, predominantly involves the brainstem and the urge-to-cough (UTC) is modulated by the cerebral cortex. Lewy body disease is associated with decreased cough reflex sensitivity and central respiratory chemosensitivity. Additionally, the insula, associated with the UTC, shows decreased activation and atrophy in dementia with Lewy bodies (DLB). We investigated the relationships between cognition and cough reflex and the UTC and compared the differences in responses of patients with DLB and other dementia subtypes. We conducted a cross-sectional study within a geriatric ward of a university hospital involving elderly patients diagnosed with Alzheimer's disease (AD), DLB, or non-dementia (controls). The cough reflex sensitivities were estimated based on the lowest concentrations of inhaled citric acid that could induce ≥2 coughs (C₂) or ≥5 coughs (C₅). Subjects were asked to rate the UTC based on the threshold concentrations (C_u) using the modified Borg scale. C₂, C₅ and C_u were negatively correlated with cognitive function in female participants but not in males (p<0.01). The cough reflex sensitivities expressed as C₂ and C₅ were significantly higher in the DLB group than in the AD and control groups (p<0.01 adjusted for gender). The UTC threshold expressed as C_u was also significantly higher in the DLB group, while the UTC log-log slope was less responsive in the DLB group than in the other groups. The cough reflex sensitivity and perceived UTC deteriorated in the DLB group more than in the other groups. This result might be valuable in treating patients with DLB.