produce enough thyroid hormones, a
condition known as hypothyroidism.
The principal symptoms of Hashimoto’s
thyroiditis are tiredness, muscle weak-
ness, and weight gain, and the thyroid
gland becomes enlarged.
Diagnosis is confirmed by blood tests.
Treatment is by thyroid hormone replace-
menttherapy, which is life-long.
hashishAnother name for marijuana.
hay feverThe popular name for a sea-
sonal form of allergic rhinitis (see
rhinitis, allergic).
HDLThe abbreviation for high density
lipoprotein.
headacheOne of the most common
types of pain. A headache is only rarely
a symptom of a serious underlying dis-
order. The pain arises from tension in
the meninges, and in the blood vessels
and muscles of the scalp.
Many headaches are simply a resp-
onse to some adverse stimulus, such as
hunger. Such headaches usually clear
up quickly. Tension headaches, caused
by tightening in the face, neck, and scalp
muscles as a result of stress or poor
posture, are also common, and may last
for days or weeks. Migraineis a severe,
incapacitating headache preceded or
accompanied by visual and/or stomach
disturbances. Cluster headachescause
intense pain behind 1 eye.
Common causes of headache include
hangoverand noisy or stuffy environ-
ments. Food additivesmay also be a
cause. Some headaches are due to over-
use of painkillers (see analgesic drugs).
Other possible causes include sinusitis,
toothache, cervical osteoarthritis, and
head injury. Among the rare causes of
headache are a brain tumour, hyper-
tension, temporal arteritis, an aneurysm,
and increased pressure within the skull.
Most headaches can be relieved by
painkillers and rest. If a neurological
cause is suspected, CT scanning or MRI
may be performed.
head-bangingThe persistent, rhythmic
banging of the head against a wall or
hard object. Head-banging is seen in
some people with severe learning dif-
ficulties, particularly those who lack
stimulation. It also occurs in some
normal toddlers, often when they are
frustrated or angry; most children grow
out of the behaviour.
head injuryInjury to the head may
occur as a result of a blow or a fall. The
severity of the injury depends on
whether the brain is affected. A blow
may shake or bruise the brain (see brain
damage). If the skull is broken (see skull,
fracture of), foreign material or bone
may enter the brain and lead to infec-
tion. A blow or a penetrating injury may
cause swelling of the brain, or tear
blood vessels, which may lead to brain
haemorrhage.
If the head injury is mild, there may
only be a slight headache. In some
cases there is concussion. More severe
head injuries may result in uncon-
sciousness or coma, which may be fatal.
Amnesiamay occur. After a severe brain
injury, there may be some muscular
weakness or paralysisand loss of sen-
sation. Symptoms such as persistent
vomiting, double vision, or a deteri-
orating level of consciousness could
suggest progressive brain damage.
Investigations may include skull X-rays
and CT scanning. A blood clot inside
the skull may be life-threatening and
requires surgical removal; severe skull
fractures may also require surgery.
Recovery from concussion may take
several days. There may be permanent
physical or mental disability if the brain
has been damaged. Recovery from a
major head injury can be very slow,
but there may be signs of progressive
improvement for several years after
the injury occurred.
head lagThe backward flopping of the
head that occurs when an infant is placed
in a sitting position. Head lag is obvi-
ous in a newborn because the neck
muscles are still weak, but by 4 months
the baby can hold his or her head up-
right (see child development).
Heaf testA type of tuberculin test.
healingThe process by which the body
repairs bone, tissue, or organ damage
caused by injury, infection, or disease.
The initial stages of healing are the
same in all parts of the body. After injury,
blood clotsform in damaged tissues.
White blood cells, enzymes, histamine,
other chemicals, and proteinsfrom whichHASHISH HEALING
H