or insomnia. Possible side effectsinclude
drowsiness, constipation, dry mouth,
dizziness, and, rarely, priapism.
treatmentAny measure that is taken to
prevent or cure a disease or disorder or
to relieve symptoms.
trematodeThe scientific name for any
flukeor schistosome.
tremblingSee tremor.
tremor An involuntary, rhythmic, oscil-
lating movement in the musclesof part
of the body, most commonly those of
the hands, feet, jaw, tongue, or head.
Tremor is the result of rapidly alternat-
ing muscle contraction and relaxation.
Occasional tremors are experienced by
most people and are due to increased
production of the hormone adrenaline
(epinephrine). A slight, persistent tre-
mor is common in elderly people.
Essential tremor, which runs in fami-
lies, is a slight-to-moderate tremor that
may be temporarily relieved by consum-
ing a small amount of alcohol or by
taking beta-blocker drugs.
Coarse tremor (4–5 muscle movements
per second), which is present at rest but
reduced during movement, is often a
sign of Parkinson’s disease. An intention
tremor (tremor that is worse on move-
ment of the affected part) may be a sign
of cerebellar ataxia. Tremor may also be
caused by multiple sclerosis, Wilson’s dis-
ease, mercury poisoning, thyrotoxicosis,
or hepatic encephalopathy; drugs, such
as amfetamines and caffeine; and with-
drawal from drugs, including alcohol.
trench feverAn infectious disease that
is now rare or unknown in most parts of
the world. The disease is caused by rick-
ettsiaespread by body lice. Symptoms
include headache, muscle pains, and
fever, which may occur in bouts. Treat-
ment is with antibiotic drugs.
trench footSee immersion foot.
trench mouth See gingivitis, acute
ulcerative.
trephineA hollow, cylindrical instru-
ment with a saw-toothed edge used for
cutting a circular hole, usually in bone.
tretinoinA topicaldrug that is chemi-
cally related to vitamin Aand is used to
treat acneand certain skin disorders
such as ichthyosis. Tretinoin may aggra-
vate acne in the first few weeks oftreatment but usually improves the
condition within 3–4 months. Possible
side effects include irritation, peeling,
and discoloration of the skin. Exposure
of the skin to sunlight while using
tretinoin may aggravate irritation and
can lead to sunburn.
trial, clinicalA test on human volun-
teers of the effectiveness and safety of a
drug. A trial can also involve systematic
comparison of alternative forms of medi-
cal or surgical treatment for a particular
disorder. Patients involved in clinical tri-
als have to give their consent, and the
trials are approved and supervised by
an ethics committee.
triamcinoloneA corticosteroid drugthat
is used to treat inflammation of the
mouth, gums, skin, and joints; asthma;
and certain blood disorders, such as
thrombocytopeniaand leukaemia.
triamtereneA diuretic drugused to
treat hypertensionand oedema. Pos-
sible adverse effects include nausea,
vomiting, weakness, and rash.
tribavirinsee ribavirin.
triceps muscleThe muscleat the back
of the upper arm. At the upper end of
the triceps are 3 “heads”; 1 is attached to
the outer edge of the scapula(shoul-
derblade), and the other 2 to either side
of the humerus(upper-arm bone). The
lower part of the triceps is attached to
the olecranon process of the ulna (the
bony prominence on the elbow). Con-
traction of the muscle straightens the
arm. (See also biceps muscle.)
trichiasisAn alteration in the direction
of eyelash growth, in which the lashes
grow inwards towards the eyeball. They
can rub against the eye, causing severe
discomfort and sometimes damage to
the cornea. Trachomais a cause.
trichinosisAn infestation with the lar-
vae of the TRICHINELLA SPIRALISworm,
usually acquired by eating undercooked
pork. Trichinosis is rare in the UK. Thor-
ough cooking of all pork products, and
freezing meat to a temperature below
–18°C for 24 hours, helps to avoid infec-
tion. Slight infestation usually causes
no symptoms. However, heavy infesta-
tion may cause diarrhoea and vomiting
within a day or two of eating the infec-
ted meat, followed by fever, swellingTREATMENT TRICHINOSIST