Skeletal Muscle Disorders (inflammatory, congenital) Flashcards
Presnetation of myotonic muscular dystrophy
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)
Anti-jo-1 antibodies are antibodies against what? What disease are they found in
Aminoacyl-tRNA-synthetase antibodies. Found in dermatomyositis + polymyositis
Becker muscular dystrophy etiology
Mutation in dystrophin gene–> partially functional dystrophin protein
Etiology of X-linked muscular dystrophy
X-linked mutation in dystrophin protein (anchors intracellular cytoskeleton of muscles to ECM)
Characterized by progressive muscle damage w/ replacement of skeletal muscle by adipose tissue
X-linked muscular dystrophy
Most common adult onset muscular dystrophy
Myotonic dystrophy
Pathophysiology of dermatomyositis
Autoantibodies against endothelial cells, activate complement and destroy capillaries leading to infarcts –> dropout of muscle cells close to affected capillaries
Difference between biopsy of dermatomyositis + polymyositis
Dermatomyositis- CD4+ infiltrates; occurs in perimysium w/ perifascicular atrophy around edges
Polymyositis- CD8+ infiltrates; occurs in endomysium (all around muscle cells)
Extra-muscular features of Duchenne muscular dystrophy
1) Cardiac dysfunction - dilated cardiomyopathies + arrhyhtmias
2) Death results from cardiac or respiratory failure
Presentation of Becker muscular dystrophy
Similar to Duchenne but later age of onset and milder sx
Motor presentation of Dermatomyositis; which muscle group usually spared?
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)
biopsy of inclusion body myositis
Muscle cytoplasmic inclusion proteins associated w/ neurodegenerative disease
Associated w/ malginancy (esp. gastric carinoma)
Dermatomyositis
Cutaneous findings of dermatomyositis
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
Motor signs + sx of Duchenne msucular dystrophy
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
Main difference in presentation between dermatomyositis + polymyositis
Dermatomyositis presents w/ a variety of skin findings; polymyositis does not
Etiology of Duchenne muscular dsytophy
X-linked DELETION of dystrophin gene- absence of protein
MHC-1 expression on muscle cells occurs in which disease
Polymyositis
When do symptoms of X-linked muscular dystrophy arise?
Between childhood/ adulthood (most commonly around 2-7); does NOT present in infancy
Biopsy of polymyositis
CD8+ lymphocyte infiltration in endomysial distribution- inflammatory cells all around muscle cells
Biopsy of Dermatomyositis
Perimysial inflammation w perifascicular atrophy; most damage around the edges
CD4+ infiltrate
Biopsy of muscle in Duchenne muscular dystrophy
Absence of dystrophin (staining)
Fatty replacement of muscle tissue
Types of X-linked muscular dystrophy
1) Duchenne Muscular dystrophy
2) Becker muscular dystrophy
Lab findings of dermatomyositis + polymyositis
1) High creatine kinase
2) Anti-Jo-1 antibodies (aminoacyl-tRNA-synthetase antibodies)
3) Anti-Mi-2 antibodies (nuclear helicase autoantibody)
4) ANA
Presentation of inclusion body myositis
Muscle weakness that can involve distal smalelr muscle groups (flexors of feet, forearm) and can be asymmetric
Etiology of myotonic muscular dystrophy
Autosomal dominant unstable TNR expansion of CTG in 3’UTR region of DMPK gene; displays anticipation
