DescriptionAn in-depth report on the causes, diagnosis, treatment, and prevention of common headaches.
Because of its high prevalence in developed nations, headaches are among the most costly diseases from lost work days and low productivity in the US and Europe. With tension headaches being the most common, it is surprising that so little scientific attention has been focused on determining the cause of this widespread problem. In any case, there does not appear to be a single cause of chronic tension-type; rather, many factors are likely involved.
Muscle Contractions and Tenderness
One of the most popular theories on the cause of tension-type headaches involves muscle contraction in the head, neck, and shoulders. There are a number of ideas about how muscle tension may produce these headaches.
Studies have suggested that tension-type headache sufferers may have higher-than-average muscle tenderness in the face and head that make them more susceptible to headache after muscle contractions. A few studies suggest that some patients with chronic headaches may be overly sensitive to pain in general or may overestimate muscle contraction pain.
One theory suggests that sustained tension or stress that produces muscle contractions in the tender areas around the skull constrict blood vessels. Blood flow is reduced so oxygen is blocked and waste matter builds up, resulting in pain.
Still, pain can last long after the muscles have relaxed and clear evidence is lacking on how or even if muscle contractions are a major cause of tension headache.
Sensitivity in the Central Nervous System and a Common Theory of Primary Headaches
Researchers are increasingly finding evidence to support factors that are common to both migraine and tension-type headache. Some research suggests that both problems may result from a continuum of abnormalities in the central nervous system (the nerves in the brain and spine). Such changes trigger a progression of symptoms starting with mild sensations, developing into tension headache, and finally, progressing in some people to a migraine.
Serotonin and Other Neurotransmitter Levels. Neurotransmitters are chemical messengers in the brain. Serotonin is a neurotransmitter (chemical messenger in the brain) that is important for sleep, well being, and other factors that affect quality of life. Abnormalities in serotonin levels have been observed in both tension-type and migraine headache sufferers. Altered levels of other neurotransmitters, importantly dopamine and stress hormones, also occur with migraine and tension-type headaches.
Dopamine, for example, may act as a stimulant of the migraine process. Some evidence suggests that certain genetic factors make people over-sensitive to the effects of dopamine, which include nerve cell excitation. Such nerve-cell over-activity could trigger the events in the brain leading to migraine. The prodromal symptoms (mood changes, yawning, drowsiness), for example, have been associated with increased dopamine activity. Dopamine receptors are also involved in regulation of blood flow in the brain.
Reduced Magnesium Levels. Magnesium deficiencies have been observed in people with both tension-type and migraine headaches. Researchers have noted a drop in magnesium levels before or during a migraine attack. Magnesium plays a role in nerve cell function; reduced levels could be a destabilizing factor, causing the nerves in the brain to misfire, possibly even accounting for the auras that many sufferers experience.
Nitric Oxide. Other research suggests that over-excitable neurons release nitric oxide, a small molecular messenger, which may be important in triggering in most primary headaches (tension-type, cluster, and migraines). Elevated levels have been observed in blood cells of patients with tension-type headache. There is some evidence that the release of this molecule in blood vessels may activate nerve pathways in the brain, muscles, or elsewhere and increase pain. More research is warranted.
Estrogen Fluctuations in Women. Tension-type headaches and migraine headaches are slightly more common in females during adolescence and adulthood. Most likely hormone fluctuations, rather than whether levels are elevated or low, trigger headaches. Some research suggests that fluctuations in estrogen levels may impact levels of serotonin and other pain-modulating substances that affect these headaches.
Inflammation in the Maxillary Nerve. Early studies suggest that some chronic tension-type and migraine headaches may be caused by inflammation in the nerve that runs behind the cheekbone (the maxillary nerve)--not around the covering of the brain. In fact, some work using ice water for reducing swelling in areas of the gums above the last upper molars has relieved some severe migraine and tension-type headaches.
Genetic factors appear to play a role in predisposing people to recurrent tension headaches. One study of twins suggested that the chances of inheriting the susceptibility to recurring headaches (both migraine and tension) were about 70% in close relatives. The trait is equal in both boys and girls. Because such headaches tend to occur in females, however, hormonal, social, psychological, or other factors must play a role in their development.
Stress and Psychological Factors
Tension-type headache has been highly associated with an intense response to stress. Some studies suggest that patients with chronic tension-type headaches have more general feelings of anxiety or depression and are less able to express their emotions, and a 2001 study indicated that patients with tension headaches tend to perceive everyday events as more stressful than those without headaches. Some research even suggests that tension-type headache victims may have some biological predisposition for translating stress into muscle contraction. Still, the link between stress and tension-type headaches is not fully understood and some evidence challenges any causal association.
Head and Neck Injuries
Whiplash, concussions, and other head and neck injuries, even mild ones, may result in persistent tension-type or migraine headaches in both adults and children. Such headaches should be treated as if they were the primary types. The risk for tension headaches may persist for years after the injury. For example, a 2002 survey of 26 year olds noted that tension headaches were significantly associated with neck or back injuries before the age of 13.
Other Major Causes of Chronic Daily Headaches
Medication Overuse (Rebound) Headache. About a third of persistent headaches--whether chronic migraine or tension-type--are medication-overuse headaches (MOHs). These are the result of a rebound effect caused by the regular overuse of headache medications. Nearly any headache medication can produce this effect. In one study of headache sufferers, MOH developed after an average of 1.7 years of regular use of triptans (18 doses a month), after 2.7 years of ergot use (37 doses as month), and after 4.8 years using pain killers (114 doses a month). It should be noted that regular use of pain killers for any chronic problem (such as arthritis) poses a 2% risk for medication-overuse headache, with risk being highest in people who already have primary headaches, especially migraines.
Chronic Migraines. In some cases, migraines naturally evolve into chronic, daily headaches referred to as transformed migraines. [For more information, seeWell-Connected Report #97, Migraine.]