cystic fibrosis. The lungs can also be
affected by allergic disorders. The most
important of these is asthma. Another
such disorder is allergic alveolitis, which
is usually a reaction to dust of plant or
animal origin. Irritation of the airways,
usually by tobacco-smoking, can cause
diseases characterized by damage to
lung tissue and narrowing of the airways
(see pulmonary disease, chronic obstruc-
tive). The lungs can also be affected by
canceroustumours; lung canceris one
of the most common cancers. Non-
cancerous lung tumours are uncommon.
Injury to a lung, usually resulting from
penetration of the chest wall, can cause
the lung to collapse (see pneumothorax;
haemothorax). Damage to the interior of
the lungs can be caused by inhalation
of toxic substances (see asbestosis;sili-
cosis). Blood supply to the lungs may be
reduced by pulmonary embolism.
Lung disorders can be investigated in
various ways, such as chest X-ray,bron-
choscopy, andpulmonary function tests.
lung function testsSee pulmonary func-
tion tests.
lung imagingTechniques that provide
images of the lungsto aid in the diag-
nosis of disease. Most lung disorders
can be detected by chest X-ray. CT scan-
ningand MRIplay an important role in
detecting the presence and spread of
lung tumours. Ultrasound scanningis
sometimes used to reveal pleural effu-
sion. Radioisotope scanningis used to
detect evidence of pulmonary embolism.
lung tumoursGrowths in the lungs.
These tumours may be either cancerous
(see lung cancer) or noncancerous.
Cancerous lung tumours are usually
associated with tobacco-smoking. Non-
cancerous tumours occur less frequently
than cancers. The most common form
of noncancerous tumour is a bronchial
adenoma, which arises in the lining of a
bronchus. Adenomas often cause bron-
chial obstruction; affected people may
also cough up blood. Treatment involves
surgical removal of the tumour. Other
rare noncancerous tumours include fib-
romas(which consist of fibrous tissue)
and lipomas(which consist of fatty tis-
sue). No treatment is necessary unless
the tumours are causing problems.lupus erythematosusAn autoimmune
disorderthat causes inflammation of
connective tissue. The most common
type, discoid lupus erythematosus (DLE),
only affects exposed areas of the skin.
The more serious form, systemic lupus
erythematosus(SLE), affects many body
systems, including the skin.
In both varieties of lupus erythemato-
sus, the symptoms periodically subside
and recur with varying severity. In DLE,
the rash starts as one or more red, cir-
cular, thickened areas of skin that later
scar. These patches may occur on the
face, behind the ears, and on the scalp.
Treatment is usually with topical corti-
costeroid drugs. SLE causes a variety of
symptoms. A characteristic red, blotchy,
butterfly-shaped rash may appear over
the cheeks and the bridge of the nose;
other symptoms include fatigue, fever,
loss of appetite, nausea, joint pain, and
weight loss. There may also be anaemia,
neurological or psychiatric problems,
kidney failure, pleurisy, arthritis, and
pericarditis. Diagnosis is made by blood
testsand sometimes a skinbiopsy.
Sufferers of mild forms of SLE may
have near normal health for many years;
treatment with corticosteroid drugsand
immunosuppressant drugscan improve
life expectancy. Other treatments are
available to treat specific features of the
disease. However, SLE is still a poten-
tially fatal disorder.
lupus pernioSarcoidosisaffecting the
skin, in which purple, chilblain-like swell-
ings appear on the nose, cheeks, or ears.
lupus vulgarisA rare form of tubercu-
losisaffecting the skin, especially on the
head and neck. Painless, clear, red-brown
nodules appear and ulcerate; the ulcers
eventually heal, leaving deep scars.
luteinizing hormoneAlso known as
LH, agonadotrophin hormoneproduced
by the pituitary gland.
luteinizing hormone-releasing hor-
moneA naturally occurring hormone,
also known as LH-RH, that is released
by the hypothalamusin the brain. This
hormone is also prepared synthetically
as a drug. Natural LH-RH stimulates
the release of gonadotrophin hormones
from the pituitary gland. Gonadotrophin
hormones control the production ofLUNG FUNCTION TESTS LUTEINIZING HORMONEL