Symptoms of CO poisoning are often non-specific and without correlation to the level of exposure. The risks of CO exposure increase in the autumn/winter with the use of poorly vented furnaces or fireplaces or wood stoves for heating purposes, coinciding with the peak of the season of influenza illness. The overlapping symptoms may lead to the misdiagnosis of acute or chronic CO poisoning as a case of “bad flu”, but CO poisoning patients are classically afebrile. Clinicians should have a high index of suspicion of CO poisoning, especially if several members in the same household present with similar clinical findings. Thompson et al. note that there is a wide range of symptoms, such as shortness of breath and blurred vision at mild levels (0-30% COHgb) to cardiac dysrhythmias, seizures, and coma at severe levels (>40% COHgb).²⁹

Acute Symptoms: 

• Headaches, dizziness, weakness, drowsiness, nausea, and vomiting, mimicking “flu-like” syndrome. Signs of more severe, life-threatening CO poisoning can include dyspnea on exertion, palpitations, confusion, poor mentation, irritability, irrational behavior, slurred speech, loss of consciousness, coma, and eventual death.¹ Delayed neuropsychological sequelae can occur as early as 24 hours after an acute exposure and symptoms can include memory loss, anxiety, depression, and impairment in attention.^{9, 26, 27,31,35}

Chronic Symptoms: 

• Studies of long-term, lower-level exposures to CO, primarily conducted in adults, suggest that these exposures can lead to neurological and cognitive deficits, even after removal of the source. In a study of adults by Mimura, it was noted that intellectual disturbances (memory, thinking, disorientation) and neurological symptoms (sensory disturbance, ataxia) persisted three decades after exposure.²¹ Other non-specific symptoms such as chronic fatigue, emotional distress, difficulty working, sleep disturbances, memory loss, vertigo, neuropathy, paresthesia, recurrent infections, polycythemia, abdominal pain, and diarrhea have been reported.^{16,26,32,33,37}
• In terms of imaging findings in CO poisoning patients, gray matter structures such as the globus pallidus and the hippocampus can be damaged; however, common findings on magnetic resonance imaging (MRI) are white matter hyperintensities as well as hippocampal atrophy.^2,3,22,33