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Synonyms
- AChR seronegative MG
- Anti-MuSK
- MG
- MG antibodies
- Myasthenia Gravis
Special Instructions
This assay currently is not available in New York state.
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This assay currently is not available in New York state. |
Expected Turnaround Time
7 - 11 days
Turnaround time is defined as the usual number of days from the date of pickup of a specimen for testing to when the result is released to the ordering provider. In some cases, additional time should be allowed for additional confirmatory or additional reflex tests. Testing schedules may vary.
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 |
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
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