Studies presented at the 11th Congress of the International Headache Society confirm earlier research that about 1% of the general population experiences medication-overuse headache. Headache specialists said that a far higher percentage of those seeking help for chronic headache suffer from medication overuse.
Guidelines were released as part of the second edition of the International Classification of Headache Disorders, which was presented at the congress. According to the description of medication-overuse headache as published in this revised classification, the condition is an "interaction between a therapeutic agent used excessively and a susceptible patient."
The best example, said the authors, is overuse of symptomatic headache drugs causing headache in the headache-prone patient.
Medication-overuse headache replaces previous terms such as rebound headache, drug-induced headache, and medication-misuse headache.
The classification states that overuse of symptomatic migraine drugs and/or analgesics is by far the most common cause of migraine-like headache and of a "mixed picture" of migraine-like and tension-type headaches that occur at least 15 days per month.
Medication overuse, according to the revised guidelines, is defined in terms of treatment days per month, such that treatment occurs at least two or three days each week, with intake of the drug on at least 10 days per month for at least three months. The headache is present on more than 15 days per month.
Another key feature of medication-overuse headache is that the headache has developed or is markedly worsened during overuse and resolves or reverts to its previous patterns within two months after discontinuation of the drug.
The definition does not apply to headache in women who take medications for five or six consecutive days for menstrually associated migraines but are treatment-free the rest of the month, acknowledged Fred D. Sheftell, MD, who participated in updating the classification. He said that if a woman took medications just four other days of the month, she would inappropriately meet the 10-days-a-month rule. For that reason, she must also be taking the drugs at least two to three days each week to meet the criteria.
Dr. Sheftell, who is Director and Co-Founder of the New England Center for Headache in Stamford, Connecticut and Associate Medical Director of the Headache Inpatient Unit at the Greenwich Hospital, said, "Despite the low prevalence in the population, the majority of patients presenting to tertiary care centers have chronic daily headache with 80% overusing acute medications."
In a recent review of cases in his group, Dr. Sheftell found "butalbital compounds to be the number one overused prescription medication from 1979 to 2002."
The Head-HUNT study of Norway involved 51,383 participants who responded to a headache questionnaire. Researchers in this cross-sectional population-based study found the prevalence of analgesic use increased with age, especially among headache sufferers and among women. The prevalence of medication-overuse headache was 1% for the population in general, but 1.3% for women and 0.7% for men.
Chronic headache, which is headache for at least 15 days per month, was more than seven times more likely among those with analgesic overuse than in those without. Analgesic overuse was most common for chronic migraine, intermediate for chronic nonmigrainous headache, and lowest for chronic neck and chronic low-back pain.
A second study was based on interviews of 4,855 people in the general population of Spain. Of those, 332 reported having headaches more than 10 days per month along with analgesic consumption, and 74 fulfilled the criteria for chronic daily headache with analgesic overuse. Mean age among the study cohort was 56. The prevalence in women was 2.6%, compared with 0.19% in men.
The mean duration of primary headache was 35 years and the mean duration of near-daily drug intake was 11 years. The prevalence was highest in participants in their 50s, among whom 5% of women fulfilled the criteria. Thirty-five percent overused simple analgesics, 22% ergotics, 12.5% opioids, 2.7% triptans, and 27% overused combinations.
The guideline authors wrote, "The diagnosis of medication-overuse headache is clinically extremely important because patients rarely respond to preventive medications whilst overusing acute medications."