MUSCLE WASTING
M
m u s c le w a s tin g
S e e
m u s c u l a r a t r o p h y
.
m u s c u la r a tro p h y
W e a k n e s s a n d s h r i n k i n g o f m u s c l e t i s -
s u e . M u s c u l a r a t r o p h y m a y h a v e m a n y
p o s s i b l e c a u s e s , i n c l u d i n g i n j u r y , s t a r v a -
t i o n ,
l o s s
o f f u n c t i o n i n a b o d y p a r t ,
d e g e n e r a t i o n o f m u s c l e c e l l s , a n d d i s o r -
d e r s o f t h e n e r v e s s u p p l y i n g m u s c l e s .
M u s c l e s c a n a t r o p h y r a p i d l y i f a b o d y
p a r t i s n o t u s e d a n d i f n o m e a s u r e s a r e
t a k e n t o p r e v e n t t h e p r o b l e m . I n a b r o -
k e n l e g , f o r e x a m p l e , m u s c l e l o s s m a y
b e v i s i b l e a f t e r o n l y a w e e k . T h e m u s c l e
f i b r e s
a r e
n o t l o s t ,
h o w e v e r ;
t h e y
c a n
r e t u r n t o n o r m a l i f t h e m u s c l e i s s t i m u -
l a t e d a n d u s e d .
m u s c u la r d y s tro p h y
A g r o u p o f r a r e i n h e r i t e d m u s c l e d i s o r -
d e r s t h a t c a u s e s l o w , p r o g r e s s i v e w a s t i n g
o f m u s c l e f i b r e s . T h i s d e g e n e r a t i o n m a y
l e a d t o d i s a b i l i t y a n d d e a t h .
TYPES AND SYMPTOMS
T h e m o s t c o m m o n a n d s e v e r e f o r m o f
m u s c u l a r d y s t r o p h y i s D u c h e n n e m u s c u -
l a r d y s t r o p h y . T h i s i s c a u s e d b y a r e c e s s i v e
g e n e c a r r i e d o n t h e X c h r o m o s o m e ( s e e
s e x - l i n k e d i n h e r i t a n c e
).
B o y s o n l y h a v e o n e
X c h r o m o s o m e , s o i f t h e y i n h e r i t a c o p y
o f t h e d e f e c t i v e g e n e f r o m t h e i r m o t h e r
t h e y d e v e l o p t h e d i s o r d e r . G i r l s ( w i t h t w o
X
c h r o m o s o m e s )
a r e
n o t
a f f e c t e d
b u t
b e c o m e c a r r i e r s o f t h e d e f e c t i v e g e n e .
A f f e c t e d
b o y s
w a l k w i t h
a
w a d d l e ,
f i n d
c l i m b i n g
d i f f i c u l t ,
a n d m a y h a v e
c u r v a t u r e
o f
t h e
s p i n e .
T h e
d i s o r d e r
p r o g r e s s e s r a p i d l y : t h e a b i l i t y t o w a l k i s
l o s t b y t h e a g e o f 1 2 , a n d f e w b o y s s u r -
v i v e b e y o n d t h e t e e n a g e y e a r s .
B e c k e r ’s
m u s c u l a r
d y s t r o p h y
s t a r t s
l a t e r i n c h i l d h o o d a n d p r o g r e s s e s a t a
s l o w e r r a t e . M
y o t o n i c d y s t r o p h y a f f e c t s
t h e m u s c l e s
o f t h e
h a n d s ,
f a c e ,
n e c k ,
a n d f e e t , a n d c a u s e s
l e a r n i n g d i f f i c u l t i e s
.
L i m b - g i r d l e m u s c u l a r d y s t r o p h y m a i n l y
a f f e c t s m u s c l e s i n t h e h i p s a n d s h o u l -
d e r s , a n d f a c i o s c a p u l o h u m e r a l m u s c u l a r
d y s t r o p h y a f f e c t s m u s c l e s i n t h e u p p e r
a r m s , s h o u l d e r g i r d l e , a n d f a c e . I n t h i s
l a s t f o r m
, s e v e r e d i s a b i l i t y i s r a r e .
DIAGNOSIS
A
d i a g n o s i s
f o r
D u c h e n n e
m u s c u l a r
d y s t r o p h y c a n b e m a d e w i t h g e n e t e s t -
i n g
b e f o r e
s y m p t o m s
d e v e l o p .
O n c e
m u s c l e w e a k n e s s h a s
d e v e l o p e d ,
o t h e r
t e s t s m a y b e
u s e d , i n c l u d i n g m e a s u r e -
m e n t o f m u s c l e
e n z y m e s
a n d a n
E M G
.
TREATMENT
T h e r e i s n o
c u r e ,
a n d
p h y s i o t h e r a p y
i s
t h e m a i n t r e a t m e n t . R e m a i n i n g a s a c t i v e
DUCHENNE MUSCULAR DYSTROPHY: A TYPICAL FAMILY TREE
Affected males always inherit the gene for the disorder from their mothers, who
are carriers of the gene but are themselves unaffected. About half the sons of
carriers are affected; the other sons are neither affected nor carriers. The daughters
of carriers have a 50 per cent chance of being carriers themselves. Complex blood
tests provide the only means of knowing whether or not a certain daughter (or
granddaughter) is a muscular dystrophy carrier.
Key
a
*
Unaffected
male
Affected
male
9
9
9
Carrier
female
Possible
carrier female
Unaffected
female
TYPES OF MUSCULAR DYSTROPHY
Duchenne muscular
dystrophy
In this type, the child is slow in
learning to sit up and walk, and
does so much later than normal.
The condition is rarely
diagnosed before the age of
three, but progresses rapidly.
Affected children tend to walk
with a waddle and have
difficulty climbing stairs. In
getting up from the floor, the
child “climbs up his legs”,
pushing his hands against his
ankles, knees, and thighs.
Sometimes there is curvature
ofthe spine. Despite their
weakness, the muscles
(especially those in the calves)
appear bulky; this is because
wasted muscle is replaced by fat.
By about the age of 12, affected
children are no longer able to
walk, few survive beyond their
teenage years, usually dying
from a chest infection or heart
failure. Affected boys often have
below-average intelligence.
Becker's muscular
dystrophy
This type produces the same
symptoms as the Duchenne
type, but starts later in
childhood and progresses much
more slowly. Patients often
reach the age of 50. Both types
of dystrophy have sex-linked
inheritance.
Myotonic dystrophy
This form affects muscles of the
face, hands, and feet. Infants
are floppy and slow to develop.
The main feature isthatthe
muscles contract strongly but do
not relax easily. Myotonic
dystrophy is associated with
cataracts in middle age,
baldness, mental retardation,
and endocrine problems. The
condition has an autosomal
dominant pattern of inheritance.
Limb-girdle muscular
dystrophy
This type takes different forms. It
starts in late childhood or early
adult life, and progression is
slow. The muscles ofthe hips
and shoulders are mainly
affected. Other nerve and
muscle conditions must be
eliminated before this form of
dystrophy can be diagnosed
confidently.
Facioscapulohumeral
muscular dystrophy
This form usually appears first
between the ages of 10 and 40;
it affects only the muscle so the
upper arms, shoulder girdle, and
face. It is inherited in an
autosomal dominant pattern.
In this form of muscular
dystrophy, progression ofthe
weakness is slow, and severe
disability is rare.
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