Diseases of Skeletal Muscle Flashcards
MYASTHENIA GRAVIS
- autoimmune disorder = antibodies destroy neuromuscular connections
usually ACh receptor sites
- affects voluntary muscles of the body, especially eyes, mouth, throat, + limbs
weakness and rapid fatigue of muscles
- more common in women <40 + men >60
- confirmed with a Tensilon test*
*(injected into the child, if the child has MG, an immediate + brief increase in muscle tone is noted)
3 Types of Myasthenia Gravis in children:
Congenital MG
**Transient neonatal MG **
Juvenile MG
Congenital MG
- very rare; non-immune form of MG
- inherited autosomal recessive disease (males + females equally affected)
- symptoms usually begin in the baby’s first year and are life-long
SYMPTOMS:
- generalized weakness in arms + legs
- delays in motor skills (crawling, sitting, walking)
- babies may have difficulty feeding; may have weak eyelids + poor head control
Transient neonatal MG
- 10-20% of babies born to mothers with MG may have a temporary form
- antibodies common in MG cross the placenta to the developing fetus
- usually lasts only a few weeks; babies are not at greater risk for developing MG later in life
SYMPTOMS:
- may be weak, with a poor suck, + may have respiratory difficulty
- A few babies may need mechanical breathing machine
Juvenile MG
- auto-immune disorder develops typically in female adolescents (esp. Caucasian females)
- life-long condition that may go in and out of remission
- about 10% of MG cases are juvenile-onset
SYMPTOMS:
- may begin gradually over weeks or months
- excessively tired after very little activity; begin to have problems chewing + swallowing
- drooping eyelids may be so severe that child cannot see
> 50% of people who develop MG, first signs/symptoms are:
- ptosis = Drooping of one or both eyelids
- diplopia = Double vision (may be horizontal or vertical)
- **Blurred vision **= may come and go
Myasthenic crisis
- life-threatening condition
- muscles that control breathing become too weak to do their jobs
- emergency treatment is NEEDED
Lupus
(Can be associated with MG)
- Disease of immune system
- symptoms include:
painful or swollen joints
hair loss
extreme fatigue
red rash on the face (typically looks like a butterfly)
NEUROGENIC DISEASES
DISORDERS OF INNERVATION
•angulated fibers
•apparent increase in nuclei
•no necrosis, regeneration, or fibrosis*
MYOPATHIC DISEASES
DISEASES EFFECTING THE MUSCLE
•random size variation
•round fibers
•centralization of nuclei
•necrosis, regeneration, +/- fibrosis, inflammation
Muscular dystrophy
(Endomysial fibrosis)
What are the 2 types?
Duchenne’s MD
- reading frame mutatuions = nonfunctioning gene
•Early childhood weakness
•Gower sign
•Calf hypertrophy
•Wheelchair dependence by age 12
•Death from cardiomyopathy with conduction defects, respiratory weakness, & pneumonia
Becker MD
- readig frame deletions = semi-functioning gene
- dystrophin present, but abnormally short due to in-frame deletions
- variety of clinical presentations and progressions, most involving at least some degree of proximal weakness
Dysferlinopathy (LGMD-2B)
- Relatively sudden onset in late teens
- Good prior muscular prowess
- Early inability to tiptoe
- Calf pain and swelling
- Very high serum CK (creatine phosphokinase)
- Inflammation may be prominent
Polymyositis
“Invasion of non-necrotic fibers”
Dermatomyositis
Complement mediated, small vessel vasculitic myopathy
Inclusion body myositis
- Time of onset generally after age 40
- Preference for quadriceps (esp. men), finger flexors, + pharyngeal muscles
- Highly variable rate of progression (older age of onset = faster progression)
- Serum CK usually less than 12x upper limit of normal
(higher values do not exclude IBM)
- H&E and /or Gomori trichrome staining
(vacuolated muscle fibers + inflammation)
Immunohistochemical staining
(paired helical filaments)
cellular heteroplasmy
(2 + types of mtDNA)
- caused by Stochastic segregation during cell dividsion
- results in a threshold effect
