Neuromuscular Junction Disease Flashcards
List four neuromuscular junction disorders.
Myasthenia Gravis
Lambert Eaton Syndrome
Botulism
Tetanus
Myasthenia Gravis:
- Age of onset; how does this differ bw men and women?
- How does it present (3)?
- At what time of day are the symptoms worse?
- Bimodal distribution F (teens-30s), M (50-70)
- Presentation: generalized, bulbar (face), ocular
- Sx worse at the end of the day (fatiguable weakness; dinural variation)
Describe the pathophysiology of MG:
What are 3 possible etiologies?
1) Direct blocking of skeletal muscle AchR
2) IgG AutoAb crosslinking–> Faster internalization and degradation of AchR
3) Complement mediated lysis of muscle end plate–> decreased invaginations, SA, room for receptors
3 ways complement mediated lysis damages the NMJ motor end plate?
- Less invaginations
- Less surface area
- Less room for receptors
In AchR AutoAb (+) MG, what percent of patients have thyme hyperplasia?
What percent have a thyme tumor?
What is the most effective treatment under these circumstances?
- 50% have thymic hyperplasia
- 10-15% have thymic tumor
**One should always consider thymectomy when treating MG; especially with paraneoplastic syndrome thymoma
What should you expect to find on reflexes and sensory exam for MG?
Normal findings
Pt with MG: sustained up gaze (30-60s) will elicit what effect?
What is the most effected muscle in EOM palsy for these patients?
^ Ptosis and medial rectus weakness
MR is usually most severely involved muscle in EOM palsy
Pt with MG: Sustained abduction of arms (120s) will elicit what effect? (2)
Patient can no longer hold arms up, OR weakness becomes apparent with subsequent manual testing
May ^ dysarthria or SOB
Pt with MG: Sustained elevation of leg while laying supine (90s) will elicit what effect? (2)
Patient can no longer hold leg up, OR weakness becomes apparent with subsequent manual testing
May ^ dysarthria or SOB
Pt with MG: Repeated rising from chair without use of arms (up to 20x) will elicit what effect? (2)
Fatigues after several attempts
Early/mild weakness–> exaggerated lean-forward and buttocks-first maneuver
Pt with MG: Counting aloud (1-50) will elicit what effects?
Enhances dysarthria (nasal, lingual, labial)
What is the gold standard form of immunologic testing done to dx MG?
In what percent of patients is this found? For what form of MG is it useless?
Describe the specificity?
AchR binding Ab test
Found in 80-85% patients, useless for isolated ocular MG
Very low false positive rate;
good specificity
Which Ab is typically seen in patients with generalized MG?
What is the function of the protein it attacks?
How frequently is it isolated in AchR binding Ab negative patients?
“Anti-Muscle Specific Tyrosine Kinase”
Attacks protein responsible for clustering AchR’s
Seen in 40% of AchR binding Ab negative patients
What was the first Ab discovered in MG?
With what type of MG is this Ab heavily associated?
When do we test for this?
Anti-striated muscle Ab
75-80% patients with thymoma asstd MG have this
Test for this in very young (ID thymoma) or very old (ID isolated abnormality) patients
How effective is repetitive nerve stimulation in dx of MG?
What should be done if RNS is normal w/ high suspicion for MG?
- RNS has very low sensitivity
- Important to do SFEMG of at least one symptomatic muscle if RNS is normal
