In 2001 the Oxford university research team discovered that in seronegative myasthenia
gravis patients (patients without acetylcholine receptor antibodies) is 40% anti MuSK positive patients.
What is MuSK?
AChR must be incorporated into the postsynaptic membrane. This needs to be functional complex of other proteins, namely muscle-specific tyrosine kinase (Musk) via agrin. Then can function normally converts nerve impulse from nerve to muscle.
This type of MG is very rare but curable.The diagnostics is more difficult (lower sensitivity of electrodiagnostic tests), progression is more serious, thymectomy has no effect, intense imunosupresive therapy may make improvement but some patients remain symptomatic.
According to antibodyes
|
antibody |
AChR+ |
MuSK+ |
Ab neg (AChR-) (MuSK -) |
|
occurrence (%) |
10% 30% 45% |
7% |
8% |
|
age of manifestation |
every under 45 above 45 |
above 1 year |
every age |
|
thymus |
thymoma hypertrophy atrophy |
normal |
hyperplasia |
|
gender M:F |
1:1 1:3 2:1 |
1:4 |
1:1 |
According to clinic manifestation
|
|
AChR+ |
MuSK+ |
|
weakness of limb muscles |
++ |
+ |
|
faciobulbar weakness |
+ |
++ |
|
weakness of extraokular muscles |
++ |
+ |
|
atrophy of
language and mimic muscles
|
- |
+ |
|
respiratory insufficiency |
+ |
++ |
|
therapeutic response to
ICHE |
80 - 90% |
30 - 50% |
|
response to thymectomy |
60 - 70% |
0 |
According to laboratory findings
|
|
AChR + |
MuSK+ |
|
rep. stimulation on limb muscles |
70 - 80 % |
35 % |
|
rep. stimulation in the facial musles |
80 - 90 % |
80 % |
|
SF EMG na končetinových svalech |
95 % |
15 -50 % |
|
SF EMG m. orbicularis oculi |
95 - 99 % |
72 % |
|
hyperplasia of thymus |
65 % |
10 - 15 % |
|
thymoma |
10 % |
published 1 case |
Articles
Basic article about anti MuSK myasthenia (Hoch et al, 2001)