Muscle Specific Kinase (MuSK) Antibodies

CPT: 83519
Updated on 09/20/2022
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Synonyms

  • AChR seronegative MG
  • Anti-MuSK
  • MG
  • MG antibodies
  • Myasthenia Gravis

Expected Turnaround Time

7 - 11 days

7 - 15 days

7 - 11 days


Related Documents


Specimen Requirements


Specimen

Serum


Volume

1 mL


Minimum Volume

0.5 mL (Note: This volume does not allow for repeat testing.)


Container

Red-top tube or gel-barrier tube


Collection

Allow a minimum clotting time of 30 to 60 minutes with serum separation within 2 hours of collection. Send serum in a plastic transport tube. To avoid delays in turnaround time when requesting multiple tests on frozen samples, please submit separate frozen specimens for each test requested.


Storage Instructions

Refrigerated or frozen


Stability Requirements

Temperature

Period

Room temperature

14 days

Refrigerated

14 days

Frozen

1 year

Freeze/thaw cycles

Stable x6

Temperature

Period

Room temperature

14 days

Refrigerated

14 days

Frozen

1 year

Freeze/thaw cycles

Stable x6

Temperature

Period

Room temperature

14 days

Refrigerated

14 days

Frozen

1 year

Freeze/thaw cycles

Stable x6

Temperature

Period

Room temperature

14 days

Refrigerated

14 days

Frozen

1 year

Freeze/thaw cycles

Stable x6

Temperature

Period

Room temperature

14 days

Refrigerated

14 days

Frozen

1 year

Freeze/thaw cycles

Stable x6


Causes for Rejection

Grossly hemolytic or lipemic sample will be rejected.


Test Details


Use

Diagnosis of muscle‐specific kinase (MuSK) myasthenia gravis.

Secondary or reflex test to aid in the diagnosis of autoimmune myasthenia gravis when first‐line tests (acetylcholine receptor antibodies) are negative.

Serial measurement of MuSK antibodies to monitor MuSK MG treatment as MuSK antibody titer correlate with disease severity.


Limitations

Immunosuppressant therapy is a common cause of false‐seronegativity. In addition, patient’s characteristic signs of myasthenia gravis maybe obscured by a superimposed steroid‐induced myopathy.

Though a positive MuSK result is specific for the diagnosis of MuSK myasthenia gravis (MG), a negative MuSK result does not rule out a MG diagnosis.


Methodology

Radioimmunoprecipitation Assay (RIPA)


Reference Interval

Musk Abs.

<1.0 U/mL

Result of 1.0 U/mL or higher are positive.

A positive result, in the context of congruent clinical findings, confirms the diagnosis of autoimmune muscle‐specific kinase myasthenia gravis.


Additional Information

Myasthenia gravis (MG) is a chronic, autoimmune disease of the motor system characterized by fatigable weakness with sensory and autonomic sparing.

MG is caused by autoantibodies against proteins of the neuromuscular junction. Most cases of generalized MG are anti-acetylcholine receptor (AChR) antibodypositive; a sub-fraction of MG patients produce antibodies against Muscle Specific receptor tyrosine Kinase (MuSK).

Of generalized MG patients who lack anti-AChR antibodies (AChR-seronegative), about 40% are positive for Muscle-Specific Kinase (MuSK) antibody.

MuSK MG accounts for 5-8% of all MG and is characterized by prominent facial, bulbar and respiratory weakness, frequent respiratory crises, and atrophy of the tongue and masseter muscles.

MuSK antibody levels have been shown to correlate with disease severity. Serial measurements may be useful to follow treatment.


References

Bartoccioni E, Scuderi F, Minicuci GM, Marino M, Ciaraffa F, Evoli A. Anti‐MuSK antibodies: Correlation with myasthenia gravis severity. Neurology. 2006 Aug 8;67(3):505‐507.16894117
Berrih‐Aknin S, Le Panse R. Myasthenia gravis: A comprehensive review of immune dysregulation and etiological mechanisms. J Autoimmun. 2014 Aug;52:90‐100.24389034
Evoli A, Padua L. Diagnosis and therapy of myasthenia gravis with antibodies to muscle‐specific kinase. Autoimmun Rev. 2013 Jul;12(9):931‐935.23535158
Huijbers MG, Zhang W, Klooster R, et al. MuSK IgG4 autoantibodies cause myasthenia gravis by inhibiting binding between MuSK and Lrp4. Proc Natl Acad Sci USA. 2013 Dec 17;110(51);20783‐20788.24297891
Oger J, Frykman H. An update on laboratory diagnosis in myasthenia gravis. Clin Chim Acta. 2015 Apr 15;444:126-131.25689792

LOINC® Map

Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
504600 MuSK Abs, Serum 57436-8 504601 MuSK Abs, Serum U/mL 57436-8

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