WHAT CAUSES TENSION AND OTHER CHRONIC DAILY HEADACHES?

Because of its high prevalence in developed nations, headaches are among the most costly diseases from lost workdays 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.

The most common cause of tension-type headaches is muscle contraction in the head, neck or shoulders.

One theory suggests that sustained tension or stress constricts blood vessels by producing muscle contractions in the tender areas around the skull. Blood flow is reduced, so oxygen is blocked and waste matter builds up, resulting in pain.

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.

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. It should be noted that a 2001 experiment using botulinum toxin A (Botox) injections to relax muscles in the areas of pain had no effect on tension headaches. This study suggests that muscle contractions themselves do not play the primary role in chronic tension-type headache.

Sensitivity in the Central Nervous System and a Common Theory of Primary Headaches
Researchers are also investigating factors that are common to both migraine and tension-type headaches. 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) that trigger a progression of symptoms starting with mild sensations, developing into tension headache, and finally progressing in some people to a migraine.

Abnormal Excitability in Nerve Cells. A numbers of studies have observed an increased excitability in the nerve cells in the brains of patients with chronic tension-type headache. One study suggested, for example, that in people with chronic tension-type headache the nerve cells become abnormally over excited in response to muscle contractions (such as from stress). The central nervous system responds to this over-excitement by signaling the blood vessels in the muscles to constrict (narrow), thereby reducing the flow of blood. When this occurs in the tender areas around the skull, headache pain results.

Serotonin and Other Neurotransmitter Levels. 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.

Magnesium Deficiencies. Another theory suggests that that low levels of the mineral magnesium may trigger muscle cramps and release of factors that cause pain. Magnesium deficiencies have been observed in people with both tension-type and migraine headaches.

Nitric Oxide. Other research suggests that over-excitable neurons release nitric oxide, a small molecular messenger, 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, and some research suggests that fluctuations in estrogen levels may impact levels of serotonin and other pain-modulating substances that effect these headaches. Women can experience persistent tension-type headaches during periods of hormonal changes including menstruation, at the beginning or end of pregnancy, and menopause. In one study, pregnant women with tension or migraine headaches experienced 80% fewer headaches during pregnancy, particularly in the middle of the pregnancy.

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, early 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
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.

Other Causes of Chronic Daily Headaches
Rebound, or Drug-Induced, Headache. About a third of persistent headaches are actually the result of the rebound effect caused by the overuse of headache medications. Usually in such cases, medications have been taken on an ongoing basis for more than three days each week. If patients stop taking these drugs, the headaches come back (referred to as rebound headaches). The patient then starts taking the drugs again. Eventually the headache simply persists and medications are no longer effective. Even after successful medication withdrawal, relapse is common, particularly with drugs that contain caffeine. In one study, nearly half of patients relapsed within four years and developed full-blown relapse headaches again.

Medications implicated in rebound headache include barbiturates, sedatives, narcotics, and migraine medications, particularly those that also contain caffeine. (Heavy caffeine use can also cause this condition.) Simple painkillers such as aspirin or ibuprofen are less likely causes of rebound headaches. [For more information see the Well-Connected Report #97, Migraine.]

Transformed Migraines. In some cases, migraines naturally evolve into chronic, daily headaches referred to as transformed migraines. [For more information see the Well-Connected Report #97, Migraine.]

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.

CAUSES OF SECONDARY HEADACHES
About 90% of people seeking help for headaches have a primary headache. The remaining cases are secondary headaches, caused by an underlying disorder that produces headache as a symptom. More than 300 conditions can cause headaches. Some of the most common are listed below.

Sinus Headaches. Many primary headaches, including migraines, are misdiagnosed as sinus headaches. Sinus headaches can occur in the front of the face, usually around the eyes, across the cheeks, or over the forehead. They are usually mild in the morning and increase during the day and are usually accompanied by fever, runny nose, congestion, and general debilitation. Sinus headaches spread over a larger area of the head than migraines, but it is often difficult to tell them apart, particularly if headache is the only symptom of sinusitis; they even coexist in many cases. Often, the visual changes associated with migraine can rule out sinusitis, but such visual changes do not occur with all migraines. (In rare cases, sinusitis can cause double vision and even vision loss, a sign of very serious infection.) [For more information, see the Well-Connected Report #62, Sinusitis.]

Headaches that Originate in the Neck. Some headaches may be caused by abnormalities of the neck muscles (called cervicogenic headaches). Nerves in the neck converge in the trigeminal nerve, which is the largest nerve in the skull. It originates in the brain stem and supplies sensation to the face. This nerve can generate pain signals to the facial area that the brain may interpret as headache. Pain is usually on one side; even if it affects both sides of the head it is usually more severe on one side. The quality of the headache may be difficult to distinguish from an aching tension headache or a mild migraine without aura. Cervicogenic headaches can result from prolonged poor posture (such as that caused by sitting in front of a computer keyboard or driving daily for long periods), arthritis, injuries of the upper spine, or abnormalities in the cervical spine (the spinal bones in the neck). Whiplash injuries involve the neck and can cause constant tension headaches, which, according to a 2001 British study, resolve within three weeks in 85% of patients.

Temporomandibular Joint Dysfunction (TMJ). Muscle contractions that cause headaches may be a result of temporomandibular joint dysfunction, which is caused by clenching the jaws or grinding the teeth (usually during sleep), or by abnormalities in the jaw joints themselves. The diagnosis is easy if chewing produces pain or if jaw motion is restricted or noisy. TMJ pain can occur in the ear, cheek, temples, neck, or shoulders.

Click the icon to see an image of temporomandibular joint dysfunction.

Glaucoma. Acute glaucoma is caused by increased pressure in the eye and requires immediate medical attention. Throbbing pain may be felt around or behind the eyes or in the forehead. Patients have redness in the eye and may see halos or rings around lights.

Brain Tumor. Fear of brain tumor is common among people with headaches, but headache is almost never the first or only sign of a tumor. Changes in personality and mental functioning, vomiting, seizures, and other symptoms are more likely to appear first. When the headache does develop, it is often worse early in the morning or may awaken the person during the night.

Neuralgia. Neuralgia is pain due to nerve abnormalities, which resemble migraines or sinus headaches when they occur in the facial area.

Hypertension. Although many people attribute headaches to high blood pressure, the weight of evidence suggests that hypertension does not cause headaches. An exception is malignant hypertension, an uncommon medical emergency in which the blood pressure abruptly rises to extreme levels, causing damage to blood vessels in the brain, heart, and kidneys.

Strokes Caused by Blood Clots or Hemorrhages. A blood clot or hemorrhage in the brain leading to a stroke can cause a severe headache, sometimes referred to as a thunderclap headache when it is very sudden and severe. The onset of such a headache, particularly if it is associated with confusion, stupor, or other neurologic symptoms, mandates prompt medical attention.

Epilepsy. Severe headaches that can last 12 hours or longer are very common in epilepsy. Migraine is particularly associated with epilepsy.

Head Injuries. It is obvious that a significant blow to the head will cause pain. In most cases, the pain is similar to tension-type headache and is treated in the same way as the primary headache. Post-injury headaches, however, can reflect serious damage, ranging from skull fractures to internal bleeding, and monitoring is important.

Disorders of the Meninges. The meninges are the membranes covering the brain and the spinal cord. Meningitis, which is an infection or irritation of these membranes, is an uncommon but potentially serious cause of severe headache. Other symptoms include nausea and stiffness or pain in the neck.

Gynecologic Problems. Many clinicians have anecdotally linked gynecologic problems, such as ovarian cysts and menstrual disorders, to chronic headaches, and new data are emerging to support this association.

Temporal (Giant Cell) Arteritis. Certain causes of headaches are unique to the elderly, such as temporal arteritis, also called giant cell arteritis. Inflammation in arteries that carry blood to the head, neck, and sometimes the upper part of the body can cause very severe headaches. The risk for this headache is highest in people older than 70, especially among women, people of European heritage, and patients with polymyalgia rheumatica.

Miscellaneous Causes of Benign Headaches. Rapid consumption of ice cream or other very cold foods or beverages is the most common trigger of sudden headache pain, which may be prevented by warming the food or drink for a few seconds in the front of the mouth before swallowing. Other common benign causes of headache include eyestrain, dental problems, allergies, systemic infections, and caffeine withdrawal. Headaches may be induced by sexual activity or intense physical exertion. Leakage from spinal cord fluid is rare but can cause headaches that may be mistaken for brain tumors.

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