Myasthenia Gravis

Question 1

What is the new classification of MG?

Answer 1

focal MG, Generalized MG, fulminant MG. to each group there are 2 sub groups- thymoma associated and nonthymoma associated. In the generalized group there are 2 more subgroups- seronegative (only dogs) and thiourylene medication associated (only cats)

Question 2

What type of antibodies exist in MG?

Answer 2

auto antibodies against acetylcholine and against the protein muscle specific kinase in dogs, in cats only auto antibodies against acetyl choline.

Question 4

what is the definition of focal MG?

Answer 4

weakness in at least one focal skeletal muscle group that is not appendicular skeletal muscle
options, facial, esophageal, pharyngeal, laryngeal

Question 5

what is the definition of generalize MG

Answer 5

appendicular skeletal muscle weakness mild to severe with or without focal involvement

Question 6

what is the definition of fulminant MG?

Answer 6

acute rapidly progressive in very severe form of generalized MG frequently but not necessary causing respiratory failure

Question 7

what is the definition of seronegative generalize mystina gravis?

Answer 7

at least two seronegative tests done one to two months apart by radioimmunoassay

Question 8

what are the proteins antibodies are formed against in non thymoma associated MG?

Answer 8

The target protein is acetylcholine receptor. some dog has antibodies against Titin and rysnodine but these are not clinical and can be used only as marker to monitor disease severity, which is similar to antibodies formed intima associated MG.

Question 9

name panel plastic syndrome of thymoma

Answer 9

thymoma associated MG

Question 10

what is the pathophysiology behind thiourylene medication associated MG?

Answer 10

this cat suffer generalized MG due to breaking tolerance to self-acetylcholine receptor and it’s reversible with discontinuing of medications

Question 11

what is the percentage of seronegative MG dogs and what are the definitions and explanations for the seronegative testing results

Answer 11

2 percentage of dogs with generalized MG are seronegative. Seronegative is defined after two tests done 1-2 months apart by a radioimmunoassay. A false negative result can be due to testing early in the course of the disease or testing after immunosuppressive treatment was started. True negative results can be due to 1)damaging the antigenic epitopes while preparing the essay and preventing their recognition by the antibodies, 2) most antibodies are associated with the skeletal muscle and the levels of the circulating antibodies decrease to normal, 3) the antibodies are against toxin binding site, 4) presence of antibodies against other parts of the post synaptic NMj like muscle specific kinase.

Question 12

name at least 5 parts of the diagnosis of MG

Answer 12

the gold standard test- NMJ Ach-R autoantibodies positive done by radioimmunoassay. skeletal muscle weakness and fatigability- supportive. *Pharmacological testing -in most- dramatic improvement after Acetylcholinesterase- inhibitors. there might be a subjective improvement with other myopathic and neuropathic mimicking MG disorders and there might be no improvement in dogs and cat especially with focal MG. *Electrophysiology *assessment for a cranial mediastinal mass with X-rays or ideally CT, incidence - 3.4% in dogs in 52% in cats *in cats inquire regarding thiourylene medications *investigate for diseases associated with MG.

Question 13

what is the recommended treatment for MG?

Answer 13

symptomatic treatment with acetylcholinesterase inhibitors, immunosuppressive treatment and supportive tx - all reported successful in all subgroups. Supportive treatment is very important due to the risk of death from aspiration pneumonia which is the most common cause of death.
in dogs it’s recommended to start symptomatic treatment with pyridostigmine and add GC if there is no clinical remission. in cats there are no recommendations. Cats are more prone to the side effect of acetylcholinesterase inhibitors.Immunosuppression with GC is considered more beneficial in cats and with less side effects( in dogs exacerbation o skeletal muscle weakness seen).
In fulminant MG (worsening due to anesthesia or surgery or aspiration pneumonia causing respiratory distress) the treatment -ICU including intubation and mechanical ventilation. can be plasmapheresis (with prednisolone->remission reported) or human IVIG ( transient clinical remission).

Question 14

name 2 possible tx for saving dogs in respiratory distress with fulminant MG

Answer 14

human IVIG and plasmapheresis. human IVIG can achieve transient clinical remission and plasmapheresis was reported to achieve remission when given with Prednisolone. Both can be used any crisis in any of the subgroups of MG

Question 15

define clinical remission and immune remission

Answer 15

Clinical remission is a resolution of the clinical signs of MG. Immune remission the resolution of clinical signs of MG concurrently with stopping the treatment and normalization of the Ach-R antibodies concentrations.

Question 16

what are the chances for immune remission in MG

Answer 16

cats from the group generalize non thymoma MG experience sometimes spontaneous immune remission so perhaps shouldn’t be treated. immune remission is common in dogs with focal or generalized non thymoma MG and then treatment can be stopped and for the long run outcome is excellent. It is not clear in cats although a report of 8/8 achieving immune remission.

Question 17

if immunosuppression is not done how do we monitor MG

Answer 17

antibodies levels

Question 18

complete thymectomy as treatment for MG. what are the success rates and advantages and disadvantages of the procedure

Answer 18

in dogs it’s recommended for immune remission, success rates are unknown. in cats, on one hand no difference was found between removal and non removal of the thymus but it’s unknown if a complete removal was done, and the only cat reported with immune remission had complete thymectomy the prognosis without removal or partial removal is less favorable compared to the non thymoma group because 1) medical treatment is needed to achieve clinical remission and immune remission isn’t possible and so aspiration pneumonia or respiratory failure are still in a danger 2) The thymoma itself is space occupying, locally invasive, send metastasize, can cause hemothorax and death - all good reasons to perform the Thymectomy. the main disadvantage is the general anesthesia and the surgery as they can cause postop exacerbation of muscle weakness and fatigability.

Question 19

immune remission can be achieved in Thiourylene medication associated MG without stopping the medication- true or false?

Answer 19

false. Only by discontinuing the medication immune remission can be achieved. the outcome is less favorable without discontinuing medication as only clinical remission can be achieved.

Question 20

what are the most common causes of death in MG?

Answer 20

Aspiration pneumonia and respiratory failure

Question 21

the mortality rate in cats is much higher than in dogs with MG true or false?

Answer 21

False. the one year mortality rate is 40-60% in dogs in 15% in cats

Question 22

what is the mortality rate for cats with generalized non thymoma MG without megaesophagus?

Answer 22

0

Question 23

what are the congenital Myashenic syndromes known in dogs and cats?

Question 24

23. Q: What is common to congenital Myasthenic syndromes?

Answer 24

A: the onset is few weeks to few months of age always less than six months old. they manifest skeletal muscle weakness and fatigue ability but there are seronegative for Ach-R receptors auto antibodies. the pathogenesis- deficient neuromuscular transmission with different locations and mechanism, clinical features and response to treatment divided to presynaptic synaptic and post synaptic

Question 25

Presynaptic CMS -onset clinical signs, physical exam findings, respond to treatment

Question 25

what genetic trait is common to the CMS?

Answer 25

all are autosomal recessive.