Bma Illustrated Medical Dictionary

Excessive sweating may be caused by hot
weather, exercise, or anxiety. In some
cases it is due to an infection, thyrotoxi-
cosis, hypoglycaemia, or a nervous system
disorder. Usually, the disorder has no
known cause, and begins at puberty,
disappearing by the mid-20s or early 30s.
If hyperhidrosis is persistent and can-
not be controlled by antiperspirants,
surgery may be considered to destroy
the nerve centres that control sweating.
hyperkalaemiaAbnormally high blood
levels of potassium, often due to failure
of the kidneys to excrete it.
hyperkeratosisThickening of the skin’s
outer layer due to an increased amount
of keratin. The most common forms of
hyperkeratosis affect small, localized
areas of skin and include corns, calluses
and warts. A rare, inherited form affects
the whole of the soles and palms. The
term hyperkeratosis may also be used
to describe thickening of the nails.
hyperlipidaemiasMetabolic disorders
that are characterized by high levels of
lipidsin the blood. Hyperlipidaemias may
be inherited or associated with another
disorder, such as hypothyroidism, diabetes
mellitus, kidney failure, or Cushing’s syn-
drome. They may also be a result of use
of corticosteroid drugs. Hyperlipidaemias
are associated with atherosclerosisand
coronary artery disease.
The signs depend on the type of hyper-
lipidaemia and may include fatty nodules
in the skin or over joints, and a white line
around the rim of the cornea. Diagnosis
depends on blood tests. Treatment aims
to reduce blood lipid levels, usually by
a low-fat diet and lipid-lowering drugs.
hypermetropiaCommonly known as
longsightedness, hypermetropia is an

error of refraction that initially causes

difficulty in seeing near objects and

then affects distance vision. Hyper-

metropia tends to run in families.

Hypermetropia is caused by the eye

being too short from front to back,

which results in images not being clearly

focused on the retina. The error is pre-

sent from birth, but symptoms generally

do not appear until later life because

the focusing power of accommodation,

which compensates for hypermetropia,

declines with age.

Glassesor contact lenseswith convex

lenses reinforce focusing power.

hypernephromaA type of kidney can-

cer, also known as renal cell carcinoma.

hyperparathyroidismOverproduc-

tion of parathyroid hormone by the

parathyroid glandsthat raises the calci-

um level in the blood (hypercalcaemia)

by removing calcium from bones. This

may lead to bone disorders, such as

osteoporosis. To try to normalize the

high calcium level, the kidneys excrete

large amounts of calcium in the urine,

which can lead to the formation of kid-

ney stones (see calculus, urinary tract).

Hyperparathyroidism is most often

caused by a small noncancerous tumour

of 1 or more of the parathyroid glands. It

may also occur when the glands be-

come enlarged for no known reason. It

usually develops after age 40 and is

twice as common in women as in men.

Hyperparathyroidism may cause de-

pression and abdominal pain. However,

often the only symptoms are those

caused by kidney stones. If hypercal-

caemia is severe, there may be nausea,

tiredness, excessive urination, confu-

sion, and muscle weakness.

HYPERMETROPIA

HYPERKALAEMIA HYPERPARATHYROIDISM

H

Light rays

from near

object

Retina

NORMAL VISION HYPERMETROPIA

Light rays

focused

on retina

Cornea

Light rays

from near

object

Lens Lens

Retina

Light rays

focused

behind

retina