NMJ Disorders (Hon) Flashcards
Myasthenia Gravis pathophysiology
defect in neuromuscular transmission by antibodies attacking the nicotinic acetylcholine receptors on the post synaptic membrane (muscle membrane)
Myasthenia Gravis is associated with what hereditary subset?
HLA-B8 and HLA-DR3
Myasthenia Gravis is often seen with what other disorders?
autoimmune (SLE, RA, thyroid disorders, DM1, crohns, etc)
Incidence of Myasthenia Gravis in men and women?
more common in younger women and older men
What are the 3 general characteristics of Myasthenia Gravis?
- excessive fatiguability (fluctuating weakness)
- Distribution of weakness (ocular muscles -ptosis/diplopia)
- Clinical response to cholinergic drugs
EMG in a Myasthenia Gravis patient?
decremental response on repetitive stimulation
What type of antibodies would you suspect to find in a Myasthenia Gravis patient?
acetylcholine receptor antibodies (anti-AChR abs)
The ice bag test is helpful for diagnosis of which NMJ pathology?
Myasthenia Gravis; apply ice to ptotic lids for 2 mins and if 2 mm improvement in ptosis then it is considered a positive test
A is a normal EMG with repetition stimulation and B is showing an EMG with decreased response on repetition stimulation as seen in Myasthenia Gravis.
Treatment for Myasthenia Gravis?
an anticholinergic (Mestinon), steroids (prednisone), can use plasma exchange/IVIg for patients in a crisis and a thymectomy has been found to be helpful
Why is it important to thoroughly consider treatment for patients with Myasthenia Gravis?
because there are LOTS of drugs that make the disease worse!
Myasthenia crisis
rapid deterioration of Myasthenia Gravis; may occur spontaneous or after infection or drug use; patient will experience aspiration, diffuse weakness, and possible respiration
MAKE SURE TO STOP ANTICHOLINERGIC MEDS!!
How should you alter the treatment plan for someone experiencing a Myasthenia crisis?
STOP ANTICHOLINERGIC MEDS!! use PLEX or IVIg
What is a big clue in clinical presentation that a patient is experiencing a cholinergic crisis and not a Myasthenia crisis?
presence of miosis and/or fasciculations
Cholinergic crisis
rapid increase in weakness from excess anti cholinesterase meds (more acetylcholine in NMJ plate); will see n/v, increased sweating/saliva, bradycardia and look for miosis and/or fasciculations
Seronegative Myasthenia Gravis
none of the typical MG antibodies are found in serum; no anti-AChR abs; check for MuSK antibodies for MuSK syndrome
What are the 3 general types of MuSK Syndrome?
- oculopharyngeal weakness
- neck, shoulder and respiratory weakness
- indistinguishable from antibody positive MG
What is the treatment for MuSK syndrome?
Poor response to anti cholinesterase medications and thymectomy; treat with PLEX, IVIg and riuximab
MuSK syndrome
similar to Myasthenia Gravis but there are no MG antibodies found in serum; no anti-AChR abs; positive for MuSK antibodies
Double seronegative MG
none of the typical MG antibodies are found in serum or the MuSK antibodies; check for anti-LRP4 antibodies; symptoms milder and there is frequent ocular involvement
Lambert-Eaton Myasthenia Syndrome (LEMS) pathophysiology
autoimmune attack against voltage-gated calcium channels (VGCC’s) on the presynaptic terminal; affects Ach release at the NMJ
Lambert-Eaton Myasthenia Syndrome (LEMS) is often associated with what?
malignancy; check for small cell carcinoma of the lung
What is the typical clinical presentation of a patient with Lambert-Eaton Myasthenia Syndrome (LEMS)?
proximal weakness, areflexia, dry mouth, strength may improve after exercise
What antibodies are you looking for in someone with Lambert-Eaton Myasthenia Syndrome (LEMS)?
voltage gated calcium channel antibodies (VGCC’s)
What is the typical EMG finding in a patient with Lambert-Eaton Myasthenia Syndrome (LEMS)?
incremental response on fast repetitive stimulation (often greater than 100%)
incremental response on fast repetitive stimulation (often greater than 100%) as seen in Lambert-Eaton Myasthenia Syndrome (LEMS)
What should you look for in a patient with Lambert-Eaton Myasthenia Syndrome (LEMS)?
look for and treat malignancy; typically small cell carcinoma of the lung
Treatment for a patient with Lambert-Eaton Myasthenia Syndrome (LEMS)?
first look for and treat malignancy
treat with acetylcholinesterase inhibitors, immunosuppression and IVIg
Botulism
toxin that blocks the presynaptic mechanisms for the release of ACh; presents with dry, sore mouth and throat, blurred vision, diplopia and n/v; watch for limb and respiratory paralysis; treat in ICU with respiratory support
Why is it cautioned against treating with the antitoxin in botulism poisoning?
the antitoxin is a horse serum product and can cause serum sickness or anaphylaxis and make the condition much worse; if can monitor patient and provide respiratory support until toxin is eliminated then patient will typically recover
