Carbon monoxide poisoning involves the colorless, odorless gas that comes from engine exhausts, furnaces, or other gas-powered equipment. People who survive carbon monoxide poisoning experience initial symptoms such as headache, nausea and confusion, but often patients will experience a carbon monoxide encephalopathy several days later. This results in a subtle, but often permanent, set of symptoms such as depression, cognitive deficits, or motor impairments.
In the brain, carbon monoxide displaces oxygen in hemoglobin binding, resulting in lowered oxygen delivery and respiration. The brain therefore becomes injured from lack of oxygen. Certain parts of the brain are particularly vulnerable because of an already limited supply of blood vessels: white matter, the basal ganglia found deep in the brain, the hippocampus, and the cortical (outer) areas of brain.
Studies that use structural imaging techniques (CT or MRI) have shown that around a third of carbon monoxide poisoning patients will show normal imaging results. However, functional imaging techniques that measure blood flow (fMRI, SPECT, or PET) can detect abnormalities not seen in structural imaging. These imaging techniques not only give a more accurate picture of initial damage, but they can also clearly illustrate the time-course of the delayed damage.
Additionally, functional imaging studies can provide a correlation of brain damage to cognitive and motor impairments, providing further confirmation of delayed symptoms. In a recent case study, a man developed parkinsonian symptoms several days after carbon monoxide poisoning. A PET scan showed damage in the substantia nigra (an area deep in the brain that is associated with Parkinsons disease) that the MRI failed to show. The clinical observance of this damage led to an excellent recovery a year and a half later, with the patient returning to work.
Hurley RA, Hopkins RO, Bigler ED, & Taber KH. Applications of functional imaging to carbon monoxide poisoning. Windows to the Brain: Insights from Neuroimaging. American Psychiatric Publishing, Inc. (2008).
Rissanen E, Paavilainen T, Virta J, et al. Carbon monoxide poisoning-induced nigrostriatal dopaminergic dysfunction detected using positron emission tomography (PET). Neurotoxicology. (March 2010).