New research shows abnormal pain processing in medication overuse headache

A new study released in this month's issue of Headache helps explain why medications designed to treat migraine can actually result in worsening of headache or medication overuse headache. Medication overuse headache—previously called rebound headache—occurs in about 1.5 percent of adults. Medication overuse headache is the exacerbation of an underlying headache disorder.

This worsening is caused by regularly using acute pain or migraine medications three or more days per week. About 65 percent of people with medication overuse headache have migraine as their underlying headache disorder. Discontinuing overused medications is the first step in treating medication overuse headache. For many people, headache frequency will decrease significantly after stopping medication overuse.

Medications most commonly causing medication overuse headache:

Regularly using pain pills or acute migraine medications causes changes in the nervous system. Researcher from Italy reported data from a new study using CO2 laser-evoked potentials to study how the brain processes pain signals in people with medication overuse headaches. The laser specifically activates pain fibers. Researchers can then study how the brain responds to pain sensations. Normally, nerves get bored of the same stimulation over and over again. So the brain reaction tends to decrease as the signal is repeated. This is called habituation. Earlier research showed that people with migraine tend to lose this habituation ability. Compared with people without migraine, the migraine brain is revved up and over-sensitive to pain signals. Another way to say this is that the migraine brain tends to be over-excitable to pain.

In the new study, CO2 laser-evoked potentials were studied in people with medication overuse headache while they were still overusing medications and then again after medications were no longer being overused. Researchers found loss of habituation when people were overusing medications. After medication overuse stopped, headaches decreased for about 60 percent of the people in this study. Testing found that habituation ability had improved as headaches decreased from daily headaches to infrequent headaches. Among those patients whose headaches did not improve after discontinuing overused medications, there was no improvement in habituation.

This study teaches several important lessons:

  • Pain processing is different in people with migraine. Migraineurs are more sensitive to pain signals than people without migraine.
  • Overusing pain medications or acute migraine drugs aggravates pain processing.
  • Medication overuse further decreases the migraine brain's ability to habituate to pain signals, making the brain even more sensitive to pain.
  • Discontinuing overused medications can result in headache reduction that coincides with improved pain processing.

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