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

-

+

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)

Clinical correlates with anti-MuSK antibodies in generalized seronegative myasthenia gravis. A. Evoli et al, Brain 2003.

The futures of myasthenia gravis with antibodies to MuSK, D Ravinic et al, J Neurol Neurosurg Psychiatry, 2005.

Patterns and severity of neuromuscular transmission failure in seronegative myasthenia gravis, Y Yemoto, J Neurol Neurosurg Psychiatry, 2005.