MUSCLE SPASM
i n
w h i c h
t h e
r a i s e d
l e v e l s
o f m u s c l e
e n z y m e a r e d u e t o t h e d e a t h o f m u s c l e
c e l l s .
E n z y m e s
l e a k e d
f r o m
t h e
h e a r t
m u s c l e d i f f e r f r o m t h o s e f r o m s k e l e t a l
m
u s c l e ; t h i s d i s t i n c t i o n h e l p s d o c t o r s t o
i d e n t i f y t h e s i t e o f t h e m u s c l e d a m a g e .
m u s c le -re la x a n t d ru g s
A g r o u p o f d r u g s t h a t a r e u s e d t o r e l i e v e
m u s c l e
s p a s m
a n d
s p a s t i c i t y
.
M u s c l e -
r e l a x a n t d r u g s a r e u s e d m a i n l y i n t h e
t r e a t m e n t o f n e r v o u s - s y s t e m
d i s o r d e r s
s u c h
a s
m u l t i p l e s c l e r o s i s
a n d
p a i n f u l
m u s c u l a r
c o n d i t i o n s s u c h
a s
t o r t i c o l l i s
.
T h e y
a r e
o c c a s i o n a l l y
u s e d
t o
r e l i e v e
m u s c l e
r i g i d i t y
d u e
t o
i n j u r y .
S o m e
t y p e s o f m u s c l e - r e l a x a n t d r u g s a r e u s e d
t o
c a u s e
t e m p o r a r y
p a r a l y s i s
d u r i n g
s u r g e r y u n d e r g e n e r a l
a n a e s t h e s i a .
M o s t m u s c l e - r e l a x a n t d r u g s p a r t i a l l y
b l o c k n e r v e s i g n a l s t h a t s t i m u l a t e m u s -
c l e c o n t r a c t i o n .
D a n t r o l e n e
,
i n c o n t r a s t ,
i n t e r f e r e s w i t h t h e c h e m i c a l a c t i v i t y i n
m u s c l e c e l l s n e e d e d f o r c o n t r a c t i o n .
T h e d r u g s m a y c a u s e m u s c l e w e a k n e s s
a n d
d r o w s i n e s s .
I n r a r e
c a s e s ,
d a n t r o -
l e n e c a u s e s l i v e r d a m a g e .
m u s c le s p a s m
S u d d e n a n d i n v o l u n t a r y c o n t r a c t i o n o f a
m u s c l e . S p a s m i s a r e a c t i o n t o p a i n a n d
i n f l a m m a t i o n a r o u n d a j o i n t . C o m m o n
c a u s e s a r e
s t r a i n
,
d i s c p r o l a p s e
( s l i p p e d
d i s c ) , a n d s t r e s s . U s u a l l y , t h e u n d e r l y i n g
c a u s e
i s
t r e a t e d .
M u s c l e - r e l a x a n t d r u g s
m a y a l s o b e n e e d e d . ( S e e a l s o
s p a s t i c i t y . )
DISORDERS OF MUSCLE
The most common muscle disorder is
injury, followed by symptoms caused
by a lack of blood supply to a muscle
(including the heart muscle).There are
also various other, rare disorders that
can affect the muscles.
Injury
Muscle injuries, such as tears and
s t r a i n s
,
are very common. They cause
bleeding into the muscle tissue. Healing
may lead to the formation of a scar in
the muscle, which shortens its natural
length. Blunt injury may result in the
formation of a
h a e m a t o m a
(a localized
collection of blood) from bleeding into
the muscle. Rarely, bone may form in a
blood clot, causing
m y o s i t i s o s s i f i c a n s
.
Impaired blood supply
Muscles depend on a good blood
supply in order to function normally.
A temporary lack of blood flow, which
is sometimes associated with severe
exertion, may cause
c r a m p
.
P e r i p h e r a l
v a s c u l a r d i s e a s e
,
in which blood vessels
in the legs (and sometimes the arms)
are narrowed, restricts the blood supply,
causing
c l a u d i c a t i o n
(muscle pain on
exercise).
A n g i n a p e c t o r i s
(chest pain
caused by lack of blood supply to heart
muscle) may occur in people with
c o r o n a r y a r t e r y d i s e a s e
.
The
c o m p a r t m e n t s y n d r o m e
is pain in
muscles as a result of pressure that
limits their blood supply. It may be
brought on by injury or exercise, and
occurs most often in athletes who have
well-developed muscles.
Infection
The most serious infection of muscle is
g a n g r e n e
,
which may complicate deep
wounds (especially those contaminated
by soil).
T e t a n u s
is acquired in a similar
way; it causes widespread muscle spasm
through the release of a powerful toxin.
Viruses (especially influenza B) may
also infect muscles (causing
m y a l g i a
),
as
may the organism causing
t o x o p l a s m o s i s
.
Lastly, a parasitic disease called
t r i c h i n o s i s
can occur in muscle tissue. This disease
results from infestation with the worm
T
r i c h i n e l l a s p i r a l i s
, which is acquired by
eating undercooked meat (usually pork).
Tumours
Various forms of tumour may originate
in the muscles. Such tumours, called
primary muscle tumours, may or may not
be cancerous. Noncancerous tumours are
called
m y o m a s
;
those affecting smooth
muscle are called
l e i o m y o m a s
,
and those
developing in skeletal muscle are called
r h a b d o m y o m a s
.
Myomas of the uterus (see
f i b r o i d s
) are among the most common of
all tumours. Cancerous tumours, called
myosarcomas, are very rare; they include
r h a b d o m y o s a r c o m a s
,
which are cancers of
the skeletal muscle.
Secondary tumours, which spread from
a primary site of cancer elsewhere in the
body, very rarely involve muscle.
Hormonal and metabolic disorders
Muscle contraction depends on the
maintenance of proper levels of sodium,
potassium, and calcium in and around
muscle cells. Any alteration in the
concentration of these substances affects
muscle function. For example, a severe
drop in the level of potassium
(
h y p o k a l a e m i a
) causes profound muscle
weakness and may stop the heart. A drop
in blood calcium (
h y p o c a l c a e m i a
) causes
increased excitability of muscles and,
occasionally,
m u s c l e s p a s m s
.
Thyroid disease is often associated with
muscle disorders, the most common of
which is swelling of the small muscles
that move the eyes, causing a bulging
eyeball (see exophtha/mos).Adrenal
failure (see
A d d i s o n ’s d i s e a s e
)
causes
general muscle weakness.
Poisons and drugs
Several toxic substances can damage
muscle tissue. Alcohol can cause
damage following a prolonged drinking
bout. Other substances that may cause
muscle damage include the drugs
c h / o r o q u i n e
and
v i n c r i s t i n e
.
Genetic disorders
These disorders include the various
forms of
m u s c u / a r d y s t r o p h y
,
which
cause progressive weakness and
disability. Some types appear at birth,
some in infancy, and some develop as
late as the fifth or sixth decade.
C a r d i o m y o p a t h y
(disease of the heart
muscle) is also inherited in some cases.
Autoimmune disorders
M y a s t h e n i a g r a v i s
is a disorder involving
the transmission of nerve impulses to
muscles; it usually begins with
drooping of the eyelids and double
vision. Other autoimmune diseases that
may affect the muscles are
/ u p u s
e r y t h e m a t o s u s
,
r h e u m a t o i d a r t h r i t i s
,
s y s t e m i c s c l e r o s i s
,
s a r c o i d o s i s
, and
d e r m a t o m y o s i t i s
.
INVESTIGATION
Muscle disorders are investigated by
EMG (electromyography), which
measures the response of muscles to
electrical impulses, and by biopsy
(removal of a sample of tissue for
analysis). In addition, blood tests may
be used to detect abnormal levels of
muscle enzymes.
M
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