Tension headaches are continuous and generalized pains felt from front to back or all around the head; they are generally less severe than migraines. Although stress is the most common cause, arthritis of the neck may also cause such a headache. Tension headaches are often experienced by migraine sufferers, and a combined form of headache exists. Alleviation of stress may reduce symptoms.

Traction headaches

Traction headaches are caused by the distortion of intracranial pain-sensitive structures. This type of headache may be caused by intracranial bleeding or tumours, brain infections, obstruction of the flow of cerebrospinal fluid, and low pressure of the fluid due to leakage after lumbar puncture. Such headaches are moderately but increasingly severe, involve the whole head, may be accompanied by a throbbing sensation, are worse with movement and coughing and on awaking, and improve as the day progresses but recur for hours.

Referred headaches

Pain may also be referred to the head (i.e., felt in the head even though the site of disease is elsewhere) by eye disorders such as glaucoma, infections or tumours of the nasal sinuses, dental infections, and arthritis of the neck.

Encephalitis

Encephalitis, an infection of the brain, may be caused by a number of microorganisms including viruses, bacteria, and fungi. In the Western world, viral encephalitis is the most common type of the disorder; it is typically caused by the herpes simplex virus. Other causes of viral encephalitis are measles, mumps, polio, rabies, and influenza.

Typical symptoms of encephalitis include the onset, over hours or days, of headache, fever, stiffness of the neck, drowsiness, and malaise. Computed tomography (CT) scanning of the head, electroencephalography (EEG), and lumbar puncture (spinal tap) may be necessary in order to diagnose the disorder. Herpes simplex encephalitis is treated with medications such as acyclovir or vidarabine.

Abscess

Cerebral abscess is caused by bacterial infection that may be carried via the bloodstream, in cases of generalized or distant infection, or may result from infection following a skull fracture. Infection produces a pus-filled abscess, usually localized close to the site of the original infection. Symptoms resemble those of viral encephalitis. EEG and CT scanning may be performed to localize and determine the source of the infection.

Cortical thrombophlebitis may result from an infection that travels along the course of the intracranial veins, which themselves are infected and thrombose, or clot. This disease can occur in the venous channels of the dura mater, resulting in infarcts of the surrounding brain and damage to contiguous cranial nerves. Cortical thrombophlebitis occurs primarily in children suffering from malnutrition and dehydration, but it also may result from some blood diseases and may occur in pregnancy. The symptoms resemble those of a cerebral abscess, but there is a greater likelihood of seizures.

Antibiotics are usually administered to treat cerebral abscesses and are chosen according to the infectious organism. Anticoagulants may be used to treat cortical thrombophlebitis. Surgery may be necessary to remove scar tissue from the abscess.

Autoimmune reactions

The human immunodeficiency virus, or HIV, causes acquired immune deficiency syndrome, or AIDS, an infection that greatly diminishes the cell-mediated immune system. Many viral, bacterial, and fungal infections occur as a result. Neurological complications include encephalitis and dementia, caused by invasion of the brain by HIV.

Following common viral infections such as measles, during bacterial endocarditis (a bacterial infection of the heart valves), or after vaccination against such diseases as smallpox, an acute neurological illness with meningeal irritation, fever, reduction in consciousness, seizures, and raised intracranial pressure may occur. This condition is known as acute toxic encephalopathy and may be an acute allergic reaction of the immune system to the preceding infection. In Reye syndrome, a variation of acute toxic encephalopathy occurring in children, the same features are present, along with persistent vomiting and acute degeneration of the liver. There is some evidence that aspirin may cause the condition, and use of the salicylate is usually not recommended in children.

Acute allergic encephalomyelitis is a similar illness that is caused by damage to the myelin sheaths of the central nervous system and occurs in the second week after vaccination or viral infection. This condition causes symptoms of encephalitis and inflammation of the spinal cord or nerve roots. Treatment with corticosteroid medications is sometimes effective.

Syphilis

Syphilis follows infection with the spirochete Treponema pallidum as a result of sexual contact with an infected individual or infection of the fetus in utero. Primary syphilis produces a chancre, or sore, at the site of infection. Weeks later, secondary syphilis develops and causes a skin rash and signs of meningitis. In the third stage, the spirochete invades the nervous system and may cause tabes dorsalis (see above The spinal cord: Inflammation) or chronic syphilitic encephalitis, which causes progressive dementia and signs of focal damage to the brain. Diagnosis of syphilis is confirmed by blood tests and by examination of the cerebrospinal fluid. Treatment with penicillin stops the progress of the disease and may relieve some of the symptoms.