PDF - NMJD Flashcards
What type of channels of on endplate at NMJ?
Nicotinic acetylcholine receptors
What happens to ACH in the NMJ?
Broken down by acetylcholinesterase
Treatment MG?
Can be improved by drugs that inhibit AChE, effectively increasing the amplitude and duration of the EPP
What happens in botulism?
Bacterial toxin binds presynaptically at NMJ, preventing ACh release = weakness
What is MG?
Autoimmune disease in which the immune system inappropriately reacts self-antigen.
- T and B-cells produce Ig blocking and destroying AChRs
faster than they can be synthesized
Where do T cells develop?
Thymus?
Common abnormalities seen in MG?
- Glandular enlargement or hyperplasia of thymus
2. Thymoma = less common
Presentation MG?
- Weakness and fatigue of skeletal muscles
2. Without pain, sensory or cognitive impairment
Most common symptoms MG?
- Ptosis (eyelid drooping)
- Diplopia (double vision from asymmetrically weak extraocular muscles)
- Dysarthria (slurred speech)
- Dysphagia (weakness of swallowing)
* **Can at times be asymmetrical
Normal Neurological signs in MG?
- Muscle stretch reflexes
2 Cognition - Higher cortical functions
- Muscle atrophy develops only rarely
What is occular MG?
Only have eye symptoms
What is In neonatal myasthenia?
Healthy newborns of myasthenic mothers may have MG symptoms for a few days, until maternal Ig “wash out”
What happens in myasthenic crisis?
Profound weakness may cause quadriplegia, with patient unable to speak, swallow or breathe.
- May be suddenly triggered by a serious infection or other systemic illness
Type of infarction that can be similar to MG?
Extensive infarction of brainstem, where hyperreflexia may be noted
GBS presentation?
Weakness developing over days with areflexia and sensory impairment accompanying
How to diagnose GBS?
- EMG
2. Elevated CSF protein
Tests for MG?
- Marked improvement after injection of an ACh-esterase inhibitor drug like edrophonium (Tensilon)
- Single fiber jitter on electromyography
- Serum AChR antibodies - Most specific
What to look for in typical MG symptoms of Ig AChR negative?
Serum Ig to MuSK (muscle specific receptor tyrosine kinase), an NMJ protein important for clustering of AChRs.
Poison with effect similar to MG?
Curare, an NMJ antagonis
Rx MG? Side effect?
- Pyridostigmine (Mestinon) ACh esterase inhibitor
- Cholinergic crisis “DUMBBELLS” - Immunosuppressants - if refractory - prednisone
- Thymectomy
- Some will simply go into remission
Rx Mg crisis?
- IVIG
- Plasmapheresis - gamma globulin component of plasma,
containing all circulating antibodies as well as anti-AChR, is physically removed
What muscles does LEMS impact?
Proximal muscles of shoulders and hips as well as trunk, mimicking weakness seen in a myopathy
Other symptoms in LEMS?
- Muscle stretch reflexes may be decreased but reappear along w/ improved strength after a brief isometric exercise
Autonomic symptoms:
- Muscle stretch reflexes may be decreased but reappear along w/ improved strength after a brief isometric exercise
- Dry mouth
- Orthostatic hypotension
- Erectile dysfunction
* Sensory deficits, cognitive symptoms, and pain not usually found
What usually causes LEMS?
Small cell carcinoma of lung
Dx LEMS?
- Presynaptic NMJ abnormalities on electromyography
2. Serum Ig to voltage-gated Ca channel
Rx LEMS?
- Treat cancer
2. Guanidine or 3,4-diaminopyridine - increase ACH
