DELTOID
DEMYELI NATION
baby's head is large in relation to the
size of the mother's pelvis, a
forceps
delivery
or
vacuum extraction
may be
required. If a vaginal delivery is impos-
sible or dangerous to the mother or the
baby, a
caesarean section is
necessary,
deltoid
The triangular muscle of the
shoulder region that forms the rounded
flesh of the outer part of the upper arm,
and passes up and over the shoulder
joint. The wide end of the muscle is
attached to the shoulderblade and the
collarbone. The muscle fibres meet to
form the apex of the triangle, which is
attached to the humerus (upper-arm
bone) halfway down its length. The cen-
tral, strongest part of the muscle raises
the arm sideways. The front and back
parts of the muscle twist the arm.
DELTOID
delusion
A fixed, irrational idea not
shared by others and not responding to
reasoned argument. The idea in a para-
noid delusion involves persecution or
jealousy. For instance, a person may
falsely believe that he or she is being
poisoned (see
paranoia).
Persistent del-
usions are a sign of serious mental
illness, most notably
schizophrenia
and
manic-depressive illness.
(See also hal-
lucination;
illusion.)
dementia
A condition characterised by
a deterioration in brain function. Demen-
tia is almost always due to
Alzheimer's
disease
or to cerebrovascular disease,
including strokes. Cerebrovascular dis-
ease is often due to narrowed or blocked
arteries in the brain. Recurrent loss of
blood supply to the brain usually results
in deterioration that occurs gradually
but in stages. A small proportion of
cases of dementia in people younger
than 65 have a underlying treatable
cause such as
head injury brain tumour,
encephalitis,
or
alcohol dependence.
The main symptoms of dementia are
progressive memory loss, disorienta-
tion, and confusion. Sudden outbursts
or embarrassing behaviour may be the
first signs of the condition. Unpleasant
personality traits may be magnified;
families may have to endure accusa-
tions, unreasonable demands, or even
assault.
Paranoia, depression,
and
delu-
sions
may occur as the disease worsens.
Irritability or anxiety gives way to indif-
ference towards all feelings. Personal
habits deteriorate, and speech becomes
incoherent. Affected people may even-
tually need total nursing care.
Management of the most common
Alzheimer-type illness is based on the
treatment of symptoms.
Sedative drugs
may be given for restlessness or para-
noia. Drugs for dementia, for example
donepezil, can slow mental decline in
some people with mild to moderate
Alzheimer's disease (see
acetylcholines-
terase inhibitors).
dementia praecox
An outdated term
for severe
schizophrenia,
especially that
affecting adolescents or young adults.
De Morgan's spots
Harmless red or
purple raised spots in the skin, consist-
ing of a cluster of minute blood vessels.
About 2 mm across, the spots usually
affect middle-aged or older people.
With increasing age, the spots become
more numerous but do not increase in
size. They may bleed if injured. Treat-
ment is unnecessary.
demyelination
Breakdown of the fatty
sheaths that surround and electrically
insulate nerve fibres. The sheaths pro-
vide nutrients to the nerve fibres and
are vital to the passage of electrical
impulses along them. Demyelination
"short-circuits" the functioning of the
nerve, causing loss of sensation, coordi-
nation, and power in specific areas of the
body. The affected nerves may be within
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