Chapter 27: Diseases of the NMJ and Skeletal Muscle Flashcards
Disorders of NMJs present with what?
Painless muscle weakness
Myastheina Gravis is associated with autoantibodies against what?
- ACh receptors on post-synaptic membrane (85% cases)
- Muscle-specific receptor tyrosine kinase (15%)
There is a strong association with tht AChR autoantibodies seen in Myathenia Gravis and which abnormalities?
Thymic abnormalities: Thymoma and Thymic hyperplasia
Myasthenia gravis patients with AChR autoantibodies usually present with what signs/sx’s?
- Fluctuating weakness that worsens with exertion and over course of day
- Diplopia** and **ptosis due to involvement of extra-ocular muscles
What electrophysiologic findings help distinguish Myasthenia Gravis and Lambert-Eaton Myasthenic Syndrome?
- M.G. = Diminished muscle responses after repeated stimulation
- L.E.M.S = Increased muscle response after repeated stimulation
What is 1st line tx for Myasthenia Gravis and what other tx’s can be used to control the sx’s?
- 1st line = Acetylcholinesterase inhibitors
- Plasmapheresis and immunosuppressives (glucocorticoids, cyclosporine, rituximab) –> ↓ autoAb titers
Lambert-Eaton Myasthenic Syndrome is an autoimmune disorder due to what?
Antibodies block ACh release by inhibiting pre-synaptic Ca2+ channel
50% of Lambert-Eaton Myasthenic Syndrome cases are associated with what underlying condition?
Malignancy; most often small-cell carcinoma of lung
Pt’s with Lambert-Eaton Myasthenic Syndrome typically present with what sx’s?
Weakness of the extremities and autonomic dysfunction
Type II fiber atrophy with sparing of type I fibers is seen with what?
Prolonged corticosteroid therapy or disuse
Clusters or groups of atrophic skeletal muscle fibers are seen in which disorders?
Neurogenic diseases
Regenerating myofibers are rich in what and stain how in H&E stained sections; characteristic nuclei and nucleoli that are seen?
- RNA and stain basophilic
- Enlarged nuclei and prominent nucleoli
Which autoantibody type in Dermatomyositis is associated with prominent Gottron papules and heliotrope rash?
Anti-Mi2 antibodies
Which autoantibody type in Dermatomyositis is associated with interstitial lung disease, non-erosive arthritis, and a rash known as “mechanic’s hands?”
Anti-Jo1 antibodies
Which autoantibody type in Dermatomyositis is associated with paraneoplastic and juvenile cases?
Anti-P155/P140 antibodies
Myofiber atrophy accentuated at the periphery of fascicles known as perfascicular atrophy is seen with what disorder?
Dermatomyositis
Biopsies and immunohistochemical studies of muscle and skin in Dermatomyositis will show deposition of what?
Complement MAC (C5b-9) within capillary beds + infiltrate rich in CD4+ T helper cells
What are the signs and sx’s of dermatomyositis and some complications which may be seen?
- Slow onset symmetric muscle weakness often w/ myalgias affecting the proximal ms. 1st
- 10% of pt’s have dysphagia and another 10% with interstitial lung disease —> can cause death
- Cardiac involvement = common, rarely leads to failure
What is the most common inflammatory myopathy in children and average age of onset?
Juvenile Dermatomyositis; average age 7 y/o