Skeletal Muscle Diseases

Question 1

Type I Fiber

Answer 1

Red 
Contraction is slower 
More prolonged 
More myoglobin
More mitochondria
Myosin ATPase: pale
Training: endurance, same size, proliferation of mitochondria

Question 2

Type II Fiber

Answer 2

White
Contraction is faster
Shorter
More powerful
Anaerobic glycolysis
dark
Training: hypertrophy
Disuse: atrophy

Question 3

Rhabdomyolysis

Answer 3

Dissolution of skeletal muscle fibers
Release of myoglobin
Acute renal failure
Acute / subacute /chronic
Heat stroke or malignant hyperthermia, alcoholism.
Noninflammatory

Question 4

Type II Fiber Atrophy

Answer 4

Mainly from disuse

Cushing syndrome

Question 5

Inflammatory Myopathies

Answer 5

Heterogeneous group
Acquired disorders
Immunologically mediated, autoimmune origin*
Systemic disease
Injury and inflammation of skeletal muscle.
Non suppurative inflammation 
		Dermatomyositis
		Polymyositis
		Inclusion body myositis 3:1

Question 6

Dermatomyositis

Answer 6

Women 20-40 years
Skin and skeletal muscle
Rash in the eyelids, face, extensor surfaces of hands and feet.
Muscle weakness: slow onset (in several weeks)
systemic, in proximal muscle, remissions and exacerbations, myalgias, fever, arthralgias, and illness
Dysphagia in 1/3 of cases
Extramuscular manifestations: vasculitis, myocarditis, lung
20-40% associated with neoplastic process

Question 7

Pathogenesis of Dermatomyositis

Answer 7

Target capillaries, ii around small vessels, in perimysial connective tissue.
Ischemic myocyte necrosis.
Abs and complement in the capillaries
B cells and CD4+ T cells
Alteration in the periphery of fascicles.
Reduction in the intramuscular capillaries
AFFECTS THE PERIMYSIUM

Question 8

Polymyositis

Answer 8

Proximal muscle
No skin component
Mainly in adults
Cell-mediated injury, CD8+ cytotoxic T cells and macrophages.
Necrosis and regeneration without perifascicular pattern
No evidence of vascular injury
Endomysial inflammation 
Angiopathy is absent
No perifascicular atrophy

Question 9

Inclusion Body Myositis

Answer 9

Males, middle age
Muscle weakness slowly progressive
Painless
Distal limb muscles and atrophy of the extensor compartment of the arm
Resistant to corticosteroid treatment
Lymph infiltration, fiber necrosis and regeneration
Clue: autophagic vacuoles and inclusion bodies
Inclusion: filaments straight or slightly curved, up to 1 µm in length and 10-25 nm in diameter

Question 10

Myasthenia Gravis

Answer 10

Ab interfere with the receptors and prevents muscle contractions

Ocular symptoms:
A drooping of one or both eyelids
Double or blurred vision
Weakness of the muscles that move the eyeballs

Oral symptoms:
Swallowing
Speaking
Breathing