Chronic exposure to carbon monoxide in two elderly patients using a kotatsu, a traditional Japanese charcoal‐based heater

We report on two elderly patients with cognitive impairments, for whom chronic carbon monoxide (CO) exposure was suspected based on elevated carboxyhaemoglobin levels in their serum. On their initial visits, cognitive impairment and brain magnetic resonance imaging findings in both patients were compatible with the diagnosis of Alzheimer's‐type dementia. However, after discontinuation of the use of a kotatsu, a charcoal‐based heater, their serum carboxyhaemoglobin levels normalized and their physical symptoms resolved. Their cognitive function also slightly improved. The causal relationship between physical symptoms and cognitive impairment after chronic CO poisoning is uncertain; however, it is possible that chronic exposure to low CO levels exacerbated the clinical manifestation in our patients.