Carbon Monoxide Poisoning Headache

Carbon monoxide poisoning (CO poisoning) is a life-threatening condition.

It is usually the result of poorly ventilated coal or oil based fires or boilers.

Occupational exposure from poorly ventilated motor vehicles like indoor forklift trucks, or in attempted suicide by car exhaust inhalation are other sources of poisoning.

If the diagnosis is not made, a patient may make a spontaneous recovery and end up returning to the source of carbon monoxide.

Ultimately, CO poisoning can be fatal or cause serious, permanent neurological injury, such as memory problems, personality change and difficulty walking or co-ordinating.

The clue to diagnosis is a new onset headache, without any obvious cause. Poisoning from carbon monoxide is more common in poorer socio-economic groups and certain occupations (you did remember to ask what your patient did for a living didn't you?).

Untreated, people with CO exposure can present in coma, and their examination may show a flushed appearance, and you make the diagnosis by measuring carboxy-haemoglobin concentrations in arterial blood.

However, a recent study of the headache characteristics of 100 people with poisoning concluded that there was not a diagnostic headache feature.

In that study, Drs Hampson found that headaches were predominantly dull (72% described the pain like this), and only in 41% was a throbbing pain reported at any point in the illness. 16% reported an intermittent headache! About 2/3rds of people reported the pain at the front of the head.

The treatment of choice is hyperbaric oxygen (the same as used by deep sea divers to prevent the bends).

In the 69 people in Hampsons' study who still had headache prior to hyperbaric oxygen, 97% found relief of pain after treatment, 44% had complete relief.

Level of pain does not correlate with carboxyhaemoglobin concentration, so severity of headache cannot be used to judge how serious the degree of poisoning is. Other symptoms can accompany poisoning with carbon monoxide like blurred vision or intolerance of noise, so it is easy to see how this new onset headache could be confused for migraine.

Like all diagnoses, and I keep saying this, you need to have an index of suspicion.

If carbon monoxide exposure is a possibility (remember that about 3% of emergency room referrals in winter may have carbon monoxide exposure) then check the carboxyHB level and treat accordingly.

References

Hampson and Hampson. Characteristics of Headache Associated With Acute Carbon Monoxide PoisoningHeadache 2002;42:220-3 (Free Abstract only)

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