DELUSION
D
passes up and over the shoulder joint.
The wide end of the muscle is attached
to the scapula (shoulderblade) and the
clavicle (collarbone). The muscle fibres
meet to form the apex of the triangle,
w hich is attached to the humerus (the
upper-arm bone) at a position about
halfway down its length.
The central, strongest part of the del-
toid muscle raises the arm sideways. The
front and back parts of the muscle are
used to twist the arm.
delusion
A fixed, irrational idea not shared by
others and not responding to reasoned
argument. The central idea in a para-
noid delusion involves persecution or
jealousy; for instance, a person may
falsely believe that he or she is being
poisoned or that a partner is persistently
unfaithful (see
paranoia
) .
Persistent delusions are an indication
of serious
mental illness,
particularly
schizophrenia
and
manic-depressive illness
.
(See also
hallucination
;
illusion
. )
demand pacemaker
A permanent artificial cardiac
pacemaker
(a device that sends electrical impulses
to the
heart
to maintain a regular
heart-
beat
)
that
discharges
impulses
only
when the
heart rate
is abnormal. Such a
pacemaker may be set to function only
if the heart rate slows, or alternatively to
override an abnormally rapid rate. (See
also
fixed-rate pacemaker
. )
demasculinization
The loss, in a male, of normal male sec-
ondary sexual characteristics (see
sexual
characteristics, secondary
) .
This includes
reduced facial hair growth, along with
testicular
atrophy
(wasting away of the
testes)
and shrinkage of the
prostate
gland. Demasculinization may occur in
a range of conditions in w hich the
testes are damaged or diseased. It may
also
result
from
disorders
such
as
cirrhosis
and
kidney failure
,
w hich inter-
fere w ith the processing in the body
of the female sex hormone
oestrogen
.
(See also
feminization
;
intersex
;
masculin-
ization
;
sex determination
. )
dementia
A condition characterized by a gener-
alized deterioration in brain function.
Dementia most commonly affects the
elderly; about
1
in
20
people over the
age of 65, and up to 1 in 5 people over
the age of 80, have the disorder.
CAUSES AND TYPES
Dementia is caused by damage to brain
tissue. It is most commonly due to
Alz-
heimer’s disease
,
w hich causes changes
in the structure and chemistry of the
brain. The second most common form
is
multi-infarct dementia
.
In this condi-
tion, narrowed or blocked arteries in
the brain deprive the tissue of blood
and
oxygen;
repeated
small
strokes
(episodes of tissue damage due to a
lack of blood) occur, causing deteriora-
tion that develops
gradually and in
stages. Other, rare forms of dementia
include Lewy body dementia (in w hich
small, spherical structures called Lewy
bodies appear in the brain tissue);
AIDS
-
related dementia; and deterioration that
occurs as a result of progressive brain
disorders such as
Parkinson’s disease
.
SYMPTOMS
The main symptoms of dementia are
progressive memory loss, disorienta-
tion,
\ n d
confusion.
The
affected
person
may
not
remember
recent
events, he or she may become easily
lost in a familiar neighbourhood, and
may be confused over days and dates.
These symptoms may come on gradu-
ally and they may be hardly noticeable
at first; in addition, the person may
cover up any problems by
confabulation
(making up explanations in order to fill
the gaps in his or her memory).
Sudden outbursts
or
embarrassing
behaviour may be the first
obvious
signs of dementia. Unpleasant person-
ality traits may be magnified; families
of those affected may have to endure
accusations, unreasonable demands, or
even assault.
Paranoia
,
depression
,
and
delusions
may occur as the disease pro-
gresses. Irritability or anxiety gives way
to indifference towards all feelings and
events. Personal care and hygiene are
neglected, and speech becomes inco-
herent. Affected people may eventually
need total nursing care.
TREATMENT
The management of the most common
Alzheimer-type illness is based on the
treatment of symptoms. The affected
person should be kept clean and well-
nourished, in comfortable surroundings
and with good nursing care.
Sedative
drugs
may be given to reduce restless-
ness or paranoid beliefs. These measures
can help to ease distress for both the
patient and their family.
For some people w ith m ild to mod-
erate Alzheimer’s disease, drug treatment
with
acetylcholinesterase inhibitors
such
as donepezil may halt the deterioration
in mental function, or may even restore
function to the level the person experi-
enced six months previously. Regardless
of treatment, however, Alzheimer’s dis-
ease is progressive, and usually leads to
death w ithin
10
years of onset.
dementia praecox
An outdated term formerly used to des-
cribe severe
schizophrenia
,
especially that
affecting adolescents or young adults.
demineralization
Excessive loss of the
minerals
calcium
and phosphate from bone. Generalized
demineralization can occur as a result
of im m obility following an illness or
injury, or may be due to a bone disease
such as
osteomalacia
.
Patchy demineral-
ization can be due to bone metastases
(cancerous tumours that have spread
from elsewhere in the body); this con-
dition causes areas of bone to weaken,
increasing the risk of
fractures
.
De Morgan’s spots
See
Campbell de Morgan’s spots
.
De Morsier’s syndrome
Also called septo-optic dysplasia, a rare
disorder that results from the abnormal
development of the
optic disc
in the eye,
the
pituitary gland
,
and parts
of the
brain. De M orsier’s syndrome causes
eye problems, including blindness in
one or both eyes, abnormal eye move-
ments such as
nystagmus
,
squint
,
and
dilation of the pupils (rather than the
normal
contraction)
in
response
to
light. Other symptoms of the syndrome
include
seizures
,
hypotonia
(poor muscle
tone), and hormonal problems, com-
monly a deficiency in growth hormone
leading to short stature.
Treatment aims to relieve symptoms
such as hormonal deficiencies, and to
provide
rehabilitation
for affected people
w ho have impaired vision.
demyelination
Breakdown of the fatty sheaths that sur-
round and electrically insulate nerve
fibres. The sheaths provide nutrients
to the nerve fibres and are vital to the
passage
of electrical
impulses along
them. Demyelination “short-circuits” the
functioning of the nerve, w hich causes
loss
of sensation,
coordination,
and
power in specific areas of the body.
The affected nerves may be w ithin the
central nervous system
(CNS), compris-
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