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MUSK Antibody

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MUSK Antibody Test

The Muscle-Specific Kinase (MuSK) Antibody Test is used to diagnose Myasthenia Gravis (MG), particularly in patients who test negative for acetylcholine receptor (AChR) antibodies. MuSK is a protein essential for neuromuscular junction function, and its antibodies can lead to muscle weakness and fatigue.

Why is the MuSK Antibody Test Done?

✅ Diagnosing Myasthenia Gravis (MG) – Especially in AChR-antibody-negative MG cases (~10-15%).
✅ Differentiating Types of MG – MuSK-positive MG often presents more severely, affecting the bulbar muscles (swallowing, speech, and breathing).
✅ Monitoring Disease Progression & Response to Treatment – Helps in tracking MG severity and treatment response.

How is the Test Performed?

🔬 Sample Type: Blood (Serum)

Interpreting MuSK Antibody Test Results

MuSK Antibody Level Interpretation Possible Diagnosis
Negative (<0.02 nmol/L or <0.05 nmol/L) No detectable MuSK antibodies Unlikely MuSK-positive MG (but AChR-MG still possible)
Positive (>0.02 or >0.05 nmol/L) MuSK antibodies detected Suggests MuSK-positive Myasthenia Gravis

📌 MuSK-MG differs from AChR-MG:

  • More severe bulbar symptoms (speech/swallowing difficulty).
  • Less response to standard MG treatments like pyridostigmine.
  • Often requires immunosuppressants (steroids, rituximab, plasmapheresis).

Next Steps After an Abnormal Test

🩺 If MuSK antibodies are detected:
✔ Confirm MG Diagnosis – Clinical exam (fatigable muscle weakness), EMG, and response to treatment.
✔ Consider Additional Tests – AChR antibodies, Electromyography (EMG), and CT scan (to rule out thymoma).
✔ Start Treatment – Corticosteroids, IVIG, plasmapheresis, rituximab for severe cases.

⚠ MuSK-MG tends to be more aggressive than AChR-positive MG and may require early immunotherapy.