Skeletal Muscle

Question 1

Dermatomyositis

Answer 1

Inflammatory disorder of skin and skeletal muscle of unkown etiology but often associated with carcinoma.
Presents as bilateral proximal muscle weakness (can’t comb hair or climb stairs), rash of upper eyelids (heliotrope rash) or malar rash, and red papules on elbows, knuckles, and knees (Gottron Papules)

See increase in creatine kinase, +ANA and Anti-Jo antibodies, perimysial inflammation (CD4+) with perifascular atrophy on biopsy

Treat with corticosteroids

Question 2

Polymyositis

Answer 2

Inflammatory disroder of skeletal muscle that resembles dermatomyositis but no skin involvement and get endomysial (CD8+) inflammation with necrotic muscle fibers

Question 3

X-Linked Muscular Dystrophy

Answer 3

Degenerative disroder characterized by muscle wasting and replacement of skeletal muscle by adipose tissue.

Duchenne Muscular Dystrophy = deletion of dystrophin gene. Get proximal muscle weakness at 1yo that progresses to involve distal muscles. See calf PSEUDOhypertrophy and increased serum creatine kinase.

Question 4

Duchenne X-Linked Muscular Dystrophy

Answer 4

deletion of dystrophin gene. Get proximal muscle weakness at 1yo that progresses to involve distal muscles. See calf PSEUDOhypertrophy and increased serum creatine kinase.

Death results from cardiac or respiratory failure as it affects myocardium

Question 5

Becker X-Linked Muscular Dystrophy

Answer 5

MUTATED (not deleted) dystrophin gene leads to milder disease

Question 6

Dystrophin

Answer 6

Important for anchoring the muscle cytoskeleton to the extracellular matrix.

Mutation are often spontaneous but the large gene size predisposes it to high mutation rate.

Question 7

Myasthenia Gravis

Answer 7

Autoantibodies against the POSTsynaptic ACh receptor at the neuromuscular junction.
More common in women
Muscle weakness that worsens with use (less ACh released with succesive twitches so cant compete with autoantibodies as much)
Tends to involve eyes = ptosis and diplopia Symptoms IMPROVE with ANTICHOLINESTERASE agents
Associated with thymic hyperplasia or thymoma (imporves with thymectomy)

Question 8

Lambert-Eaton Syndrome

Answer 8

Antibodies against PRESYNAPTIC Calcium Channels of NMJ
Arises as a paraneoplastic syndrome (small cell carcinoma of lung)
Leads to impaired ACh release
Proximal muscle weakness that improves with use
Eyes are usually spared
DOES NOT improve with ANTICHOLINESTERASE agents
Resolves with resection of cancer

Question 9

Lipoma

Answer 9

Benign tumor of adipose tissue.

Most common soft tissue tumor in adults

Question 10

Liposarcoma

Answer 10

Malignant tumor of adipose tissue and most common malignant soft tissue tumor in adults.
see LIPOBLAST

Question 11

Rhabdomyoma

Answer 11

Benign tumor of skeletal muscle.

Cardiac Rhabdomyoma associated with tuberous sclerosis

Question 12

Rhabdomyosarcoma

Answer 12

Malignant tumor of skeletal muscle and is most common malignant soft tissue tumor in children. RHABDOMYOBLAST and DESMIN +
Usually seen in head and neck but vagina is classic site in young girls.