Skeletal Muscle & PNS Pathology Flashcards
1
Q
Normal Muscle
Beehive is normal
A
Normal Muscle
Checkerboard is normal
- Grouping is abnormal ⇒ indicates denervation with reinnervation
2
Q
What are the pathologic reactions of muscle (3)?
A
-
Hypertrophy
- Occurs secondary to increased load due to exercise or pathologic condition
-
Degeneration/necrosis
- Destruction of all or part of a myofiber; stimulates infiltration by macrophages
-
Regeneration
- Satellite cells around degenerated fiber proliferate. Regenerating fiber has bluish color
3
Q
Describe denervation atrophy (neurogenic atrophy)
A
- Clusters of fibers (of one type) become smaller and develop angular contours (group atrophy)
-
Lack of neural input results in:
- Breakdown of myosin and actin
- Resorptionof myofibrils
- Decrease in cell size
- Both type 1 and type 2 fiber clusters are found
4
Q
Describe reinnervation:
A
- **Neighboring axons sprout and reinnervate denervated myocytes **
- Fiber assumes fiber type conferred by the neighboring axon
- This causes fiber type grouping
5
Q
Neurogenic vs. Myopathic
A
Neurogenic
- bimodal size distribution
- angulated fibers
- apparent increase in nuclei (nuclear clumps)
- no necrosis, regeneration, fibrosis, or inflammation
Myopathic
- random size variation
- round fibers
- centralization of nuclei
- necrosis, regeneration, +/-fibrosis, inflammation
6
Q
List the motor neuron diseases:
A
-
Amyotrophic Lateral Sclerosis (ALS)
- Aka Lou Gehrig’s disease
- Motor Neuron Disease
- Spinal Muscular Atrophy (SMA)
7
Q
ALS
- Definition:
- Pathogenesis:
- Onset:
A
- Progressive, neurodegenerative d/o
-
UMN + LMN degeneration;
- normal sensation
- Onset: 50-60y of age (avg)
8
Q
What are the clinical s/s of ALS?
A
-
Weakness
- Muscle atrophy of affected body part
- Dysphagia, dysarthria
-
Fasciculations
- Affected body part, tongue
- Hyperreflexia
- Positive Babinski
- Spasticity
-
Pseudobulbar palsy
- Emotional lability
- Executive dysfunction
9
Q
Spinal Muscular Atrophy (SMA)
- Definition:
- Incidence:
- Demographics:
- Etiology:
A
- Degenerative LMN d/o of childhood>>adulthood
- 2nd most common autosomal recessive disorder
- Panethnic
- Homozygous deletion of exon 7 of SMN1 (survival motor neuron) gene
10
Q
What are the clincal s/s of SMA?
A
- Proximal muscle weakness >>> distal
- Dysphagia ⇒ GT
-
Respiratory weakness ⇒ hypercapnia ⇒ death
- Diaphragm failure
- Intercostal weakness
- Normal intellect
- Areflexic on exam
- Different subtypes—infantile, older infant, childhood, adult onset
11
Q
Werdnig Hoffmann Disease
A
- Large groups of rounded atrophic fibers (panfascicular atrophy)
- Sparse scattered markedly hypertrophic fibers
- Differs from typical pattern of neurogenic atrophy seen in adults
12
Q
List the muscular dystrophies:
A
-
X-linked muscular dystrophies
- Duchenne MD (DMD)
- Becker MD (BMD)
-
Autosomal Muscular dystrophies
- Myotonic MD (DM)
13
Q
Why is dystrophin important to the pathogenesis of muscular dystrophies?
A
- Mutation in Xp21
- Deletion of ≥1 exons in DMD; duplications; stop codons
- LARGEST gene in humans
- Reason that 1/3rd of cases are new mutations
- Size of dystrophin does NOT matter as much as quantity of dystrophin does
14
Q
DMD vs BMD
A
- DMD ⇒ 99% have none/nearly no dystrophin
-
BMD ⇒ 85% have abnormal dystrophin in reduced quantity
- 15% have normal dystrophin in reduced quantity
15
Q
What are the clinical s/s of DMD?
A
- Proximal muscle weakness
- Intact milestones or slightly delayed
- Gower’s maneuver
- Face/Eyes SPARED
- CK ↑↑↑ > 10,000
- Slower movement than peers ⇒ wheelchair bound by 11-12y
- Large calves
- Waddling
- Scapular winging
- Contractures
- Dilated cardiomyopathy
- Intellectual impairment (average IQ 85)
17
Q
Which lane represents DMD?
A
Lane 4: DuchenneMD: essentially no dystrophin protein present
