B6.020 Prework 2: Muscular Dystrophies

Question 1

signs of M.D. in a newborn

Answer 1

floppy infant
often preterm
poor head control
poor feeding
prolonged labor
maternal complications

Question 2

signs of M.D. in child development

Answer 2

delay in milestones

Question 3

signs of M.D. in teens/adults

Answer 3

difficulty in self care, swallowing, athletic/endurance activity

Question 4

things to check on ROS for MD

Answer 4

school functioning/cognitive development
cardiac function/ arrhythmias/ syncope
respiratory

Question 5

things to check on physical exam when suspicious of MD

Answer 5

signs of wasting or hypertrophy/ pseudohypertrophy
muscle strength
hyper vs hypotonia in weak areas
deep tendon reflexes
normal sensation
joint contracture

Question 6

what is MD

Answer 6

group of genetic disorders that are characterized by progressive loss of muscle integrity, wasting, and weakness
characterized by degeneration and regeneration of muscle fibers (in contrast with static or structural myopathies)

Question 7

populations with higher prevalence of MD

Answer 7

French Canadians in Quebec

Israeli Bukharan Jews

Question 8

signs of Duchenne and Becker MD

Answer 8

• normal milestones until walking begins
• toe walking, waddling gait, difficulty climbing stairs
• progressive difficulty rising from floor or chair
• Gowers sign @ 3
• Trendelenburg gait @ 6
• pseudohypertrophy of calf muscles
• contractures of heel cords
• kyphosis and scoliosis during childhood
• decline in lung function (adolescence)
• progressive cardiomyopathy (Becker)
• intellectual impairment in 25%

Question 9

forms of myotonic dystrophy (DM)

Answer 9

DM1 and DM2
-different genes both AD inheritance
DM1 more common
combined prevalence: 1/8000
underlying common molecular pathogenesis despite different genes
extreme variability in penetrance of specific symptoms exist in the patient population

Question 10

hallmark features of DM

Answer 10

myotonia
cataracts
cardiac conduction defects

Question 11

major differences between DM1 and DM2 presentation

Answer 11

• more ptosis in DM1

- distal and facial involvement absent in DM2 (proximal involvement sooner)

Question 12

types of DM1

Answer 12

1. mild (50 to 150 repeats)
2. classic (150 to 1000 repeats)
3. congenital (>1000 repeats)

Question 13

appears of patient with severe DM1

Answer 13

tent shaped mouth
facial diplegia
indistinct or nasal speech
dull expression
frontal balding with temporal wasting
ptosis

Question 14

diagnostic challenge of DM1

Answer 14

wide spectrum of manifestations

many not clearly related to skeletal muscle

Question 15

MSK symptoms of DM1

Answer 15

muscle weakness: distal limb, facial, axial
distal distribution is exception to general rule of other myopathies having proximal involvement and neuropathies typically having distal
rare to lose ambulation (splints or bracing)
myotonia

Question 16

what is myotonia

Answer 16

slow relaxation of muscle after contraction
usually detectable at age 5
severity of myotonia does not parallel the degree of weakness
NOT painful

Question 17

neurological symptoms of DM1

Answer 17

cognitive deficit varies from none to marked
-worse w congenital
cataracts
excessive daytime somnolence

Question 18

endocrine symptoms of DM1

Answer 18

insulin resistance

gonadal atrophy

Question 19

GI symptoms of DM1

Answer 19

smooth muscle involvement: slow gastric emptying, poor peristalsis, constipation
cholecystitis

Question 20

CV symptoms of DM1

Answer 20

usually heart block in Purkinje conduction system and arrhythmias rather than cardiomyopathy
-ECG abnormalities in 37-80%

Question 21

who is at risk of congenital DM

Answer 21

infants born to mothers with symptomatic DM

>1000 repeats in DMPK gene

Question 22

symptoms of congenital DM

Answer 22

clubfoot and contractures
generalized hypotonia and weakness at birth
facial wasting 
require gavage feeding or vent support
severe GI problems
*emergent action required

Question 23

mortality of congenital DM

Answer 23

16-41% in neonatal period

contributors to reduced survival: resp failure and elective withdrawal of care

Question 24

demonstration of myotonia on physical exam

Answer 24

sharp percussion of muscle with a reflex hammer or after firm voluntary contraction elicits sustained involuntary contraction
fades slowly over a matter of seconds

Question 25

describe the process of EMG

Answer 25

needle is inserted in a muscle
electrical activity is recorded while muscle is contracting and resting
denervated muscles have increased abnormal activity like fibrillation and there is decreased interference pattern with contraction
narrows Ddx by excluding primarily neuro processes

Question 26

nerve conduction studies

Answer 26

peripheral nerve stimulated w shocks at several points along its course to a muscle
time to initiation of contraction is recorded
determines conduction velocity (often slowed in neuropathy)

Question 27

importance of CK in muscular dystrophy

Answer 27

D/BMD values in thousands

DM -normal or mild elevation

Question 28

other lab abnormalities in MD

Answer 28

liver enzymes and LDH often elevated

histo features on biopsy

Question 29

genetics of D/BMD

Answer 29

deletions of DMD gene clusters around 2 hot spot regions

-multiplex PCR amplifies these regions, detects > 98% of deletions

Question 30

genetics of DM

Answer 30

PCR of repeat region to determine presence/extent of expansion