MSCT Week 3: Skeletal Muscle Pathology

Question 1

Satellite Cells

Answer 1

Myofiber associated stem cells called satellite cells that can contribute to regeneration following injury

Question 2

ONE SLOW RED OX

Answer 2

• Type 1
• Dark meat red legs these are high in oxidative activity, low in glycolytic capacity and red grossly because of high myoglobin and mitochondrial content
• they contract slowly but are capable of continuous and repeated contraction

Question 3

Two Fast White Sugar

Answer 3

• Type II
• White meat
• low in oxidative activity
• high in glycolytic capacity
• fast contracting
• cannot maintain repeated contraction

Question 4

Neurogenic Atrophy

Clinical Clues

Answer 4

Nerve Damage (often associated with sensory features)

Question 5

Neurogenic Atrophy

Histopathologic Features

2 Listed

Answer 5

• Fiber Type Grouping
• Group Atrophy

Question 6

Neurogenic Atrophy

Etiology

Answer 6

Motor Nerve Damage

Question 7

Disuse/Steroid Atrophy

Clinical Clues

3 Listed

Answer 7

• Bedridden/ICU
• Corticosteroids
• Hyperthyroidism

Question 8

Disuse/Steroid Atrophy

Histopathologic Features

Answer 8

Type II myofiber atrophy

Question 9

Disuse/Steroid Atrophy

Etiology

Answer 9

Atrophy of Fast Twitch Fibers

Question 10

Dystrophin Related Myopathy

Clinical Clues

Answer 10

Childhood onset

Question 11

Dystrophin Related Myopathy

Histopathologic Features

5 Listed

Answer 11

• Myofiber size variability
• Necrosis
• Regeneration
• Endomysial fibrosis
• Fatty Replacement

Question 12

Dystrophin Related Myopathy

Etiology

Answer 12

• Hereditary abnormalities of dystrophin or related proteins
• DMD gene

Question 13

Inflammatory Myopathy

Clinical Clues

2 listed

Answer 13

• Adult-onset
• associated rheumatologic features

Question 14

Inflammatory Myopathy

Histopathologic Features

3 listed

Answer 14

• Inflammation (usually T-cells)
• Necrosis
• Regeneration

Question 15

Inflammatory Myopathy

Etiology

Answer 15

Autoimmune

Question 16

Congenital Myopathy

Clinical Clues

2 Listed

Answer 16

• Onset at birth
• Floppy Infant

Question 17

Congenital Myopathy

Histopathological Features

Answer 17

Wide variety of specific changes or inclusions etc (nemaline rods, central cores)

Question 18

Congenital Myopathy

Etiology

Answer 18

Variable

Question 19

Channelopathies

Clinical Clues

2 listed

Answer 19

• Myotonia
• intermittent symptoms

Question 20

Channelopathies

Histopathologic Features

Answer 20

May be normal

Question 21

Channelopathies

Etiology

Answer 21

Muscle Sodium channel protein SCN4A defect

Question 22

Patterns of myopathic conditions

Answer 22

often associated with scattered myofiber necrosis and regeneration

Question 23

Patterns of Inflammatory myopathic conditions

Answer 23

Are myopathic but are also characterized by inflammatory infiltrates and/or intracellular inclusions

Question 24

Patterns of Fiber type Grouping and Grouped Atrophy, target Fibers conditions

Answer 24

Neuropathic changes

Question 25

Patterns of Type II Myofiber Atrophy conditions

Answer 25

* Disuse atrophy due to any cause (prolonged bed rest in the sick, casting of a bone, can cause focal or generalized muscle atrophy, which tends to affect type II fibers more than type I * Glucocorticoid exposure, whether exogenous or endogenous (Cushing's Syndrome) can also cause muscle atrophy * Hyperthyroidism can also result in Type II myofiber atrophy

Question 26

Muscular Dystrophies

Answer 26

include a variety of diseases associated with the dystrophin-glycoprotein complex

Question 27

dystrophin-glycoprotein complex

Answer 27

consists of skeletal muscle membrane-associated proteins involved in the mechanical stabilization and signalling interactions between the cytoskeleton, membrane, and extracellular matrix

Question 28

Histology of DMD and BMD 2 listed

Answer 28

* progressive replacement of muscle tissue by fibrosis and fat is the result of degeneration outpacing repair (fibrosis and fatty replacement) * As a result of ongoing repair muscles typically show marked variation in myofiber size and abnormal internally placed nuclei

Question 29

DMD and BMD in cardiac muscles

Answer 29

BMD and DMD also affect cardiac muscles

Question 30

BMD and DMD pathogenesis

Answer 30

* loss-of-function mutations in the dystrophin gene located on the short arm of the X chromosome (Xp21) * Severity of the disease correlates with the degree of the dystrophin deficiency

Question 31

Clinical features of DMD

Answer 31

* Clumsiness and inability to keep up with peers due to muscle weakness * weakness usually begins in the pelvic girdle and moves to the shoulder girdle * enlargement of calf muscles (pseudohypertrophy) * owing to ongoing muscle degeneration, high serum creatine kinase levels at birth but slowly decrease as muscle mass is lost

Question 32

Clinical Features of BMD

Answer 32

* symptomatic later in childhood or adolescence * nearly normal life-span * cardiac involvement can be the dominant feature and may result in death even in the absence of muscle weakness

Question 33

Other X linked and Autosomal muscular dystrophies

Answer 33

* Myotonic Dystrophy * Limb-girdle Muscular Dystrophy * Emery-Dreifuss Muscular Dystrophy * Fascioscapulohumeral Dystrophy

Question 34

Congenital myopathies examples

Answer 34

* Central Core Disease * Nemaline Myopathy * Centronuclear Myopathy

Question 35

Channelopathies, Metabolic Myopathies, Mitochondrial Myopathies

Answer 35

due to defects in ion channels characterized by myotonmia, relapsing episodes of hypotonic paralysis assocated with abnormal serum potassium levels or both

Question 36

Muscle Sodium Channel Protein and chromosome

Answer 36

SCN4A Chromosome 7

Question 37

Malignant Hyperthermia

Answer 37

a rare syndrome that can result in death from anesthetic agents or succinylcholine during surgery

Question 38

Mitochondrial Myopathies

Answer 38

stem from mutations in either the mitochondrial or nuclear genomes, usually manifest in early adulthood with proximal muscle weakness and sometimes severe involvement of the ocular musculature some show aggregates of abnormal mitochondria (ragged red fibers)

Question 39

Glycogen synthesis abnormalities are detected with

Answer 39

PAS and myophosphorylase

Question 40

Lipid abnormalities are detected with

Answer 40

Oil Red O

Question 41

Inflammatory myopathies

Question 42

Myotonia

Answer 42

inability to relax voluntary muscle after vigorous effort.