Muscle Specific Kinase (MuSK) Antibodies

Serum

1 mL

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

Red-top tube or gel-barrier tube

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.

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.

Radioimmunoprecipitation Assay (RIPA)

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.

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.