Skeletal Muscle Disorders (inflammatory, congenital)

Question 1

Presnetation of myotonic muscular dystrophy

Answer 1

Motor:

• Muscle wasting/ weakness
• Myotonia (hypercontractility of muscle)

Extra-muscular manifestations: CTG

• C: Cataracts
• T: Toupee (early balding in men)
• G: gonadal atrophy (testicular atrophy)

Question 2

Anti-jo-1 antibodies are antibodies against what? What disease are they found in

Answer 2

Aminoacyl-tRNA-synthetase antibodies. Found in dermatomyositis + polymyositis

Question 3

Becker muscular dystrophy etiology

Answer 3

Mutation in dystrophin gene–> partially functional dystrophin protein

Question 4

Etiology of X-linked muscular dystrophy

Answer 4

X-linked mutation in dystrophin protein (anchors intracellular cytoskeleton of muscles to ECM)

Question 5

Characterized by progressive muscle damage w/ replacement of skeletal muscle by adipose tissue

Answer 5

X-linked muscular dystrophy

Question 6

Most common adult onset muscular dystrophy

Answer 6

Myotonic dystrophy

Question 7

Pathophysiology of dermatomyositis

Answer 7

Autoantibodies against endothelial cells, activate complement and destroy capillaries leading to infarcts –> dropout of muscle cells close to affected capillaries

Question 8

Difference between biopsy of dermatomyositis + polymyositis

Answer 8

Dermatomyositis- CD4+ infiltrates; occurs in perimysium w/ perifascicular atrophy around edges

Polymyositis- CD8+ infiltrates; occurs in endomysium (all around muscle cells)

Question 9

Extra-muscular features of Duchenne muscular dystrophy

Answer 9

1) Cardiac dysfunction - dilated cardiomyopathies + arrhyhtmias
2) Death results from cardiac or respiratory failure

Question 10

Presentation of Becker muscular dystrophy

Answer 10

Similar to Duchenne but later age of onset and milder sx

Question 11

Motor presentation of Dermatomyositis; which muscle group usually spared?

Answer 11

Motor:

1) Proximal, symmetrical weakness/ myalgia involving large muscles groups (climbing stairs, combing hair, raising arms above head, etc.)
2) Neck extensor muscles- “head drop”

* ocular muscles are spared (vs. myasthenia gravis)

Question 12

biopsy of inclusion body myositis

Answer 12

Muscle cytoplasmic inclusion proteins associated w/ neurodegenerative disease

Question 13

Associated w/ malginancy (esp. gastric carinoma)

Answer 13

Dermatomyositis

Question 14

Cutaneous findings of dermatomyositis

Answer 14

1) Gottron papules- raised, scaly, red/violaceous rash on elbow, knuckles, knees
2) Heliotrope rash- rash of upper eyelids
3) Malar rash
4) Mechanic’s hands- cracking of finger pad skin
5) V-neck or shawl pattern rash- lesions in upper chest, back, base of neck

Question 15

Motor signs + sx of Duchenne msucular dystrophy

Answer 15

1) Clumsiness, difficult climbing, running, jumping
2) Waddling gait w/ Gowers sign
3) Delayed developmental milestones (speaking, sitting, waling)
4) calf pseudohypertrophy

Pts are wheelchair bound by 12

Question 16

Main difference in presentation between dermatomyositis + polymyositis

Answer 16

Dermatomyositis presents w/ a variety of skin findings; polymyositis does not

Question 17

Etiology of Duchenne muscular dsytophy

Answer 17

X-linked DELETION of dystrophin gene- absence of protein

Question 18

MHC-1 expression on muscle cells occurs in which disease

Answer 18

Polymyositis

Question 19

When do symptoms of X-linked muscular dystrophy arise?

Answer 19

Between childhood/ adulthood (most commonly around 2-7); does NOT present in infancy

Question 20

Biopsy of polymyositis

Answer 20

CD8+ lymphocyte infiltration in endomysial distribution- inflammatory cells all around muscle cells

Question 21

Biopsy of Dermatomyositis

Answer 21

Perimysial inflammation w perifascicular atrophy; most damage around the edges

CD4+ infiltrate

Question 22

Biopsy of muscle in Duchenne muscular dystrophy

Answer 22

Absence of dystrophin (staining)

Fatty replacement of muscle tissue

Question 23

Types of X-linked muscular dystrophy

Answer 23

1) Duchenne Muscular dystrophy
2) Becker muscular dystrophy

Question 24

Lab findings of dermatomyositis + polymyositis

Answer 24

1) High creatine kinase
2) Anti-Jo-1 antibodies (aminoacyl-tRNA-synthetase antibodies)
3) Anti-Mi-2 antibodies (nuclear helicase autoantibody)
4) ANA

Question 25

Presentation of inclusion body myositis

Answer 25

Muscle weakness that can involve distal smalelr muscle groups (flexors of feet, forearm) and can be asymmetric

Question 26

Etiology of myotonic muscular dystrophy

Answer 26

Autosomal dominant unstable TNR expansion of CTG in 3’UTR region of DMPK gene; displays anticipation