MuSK-Positive Myasthenia Gravis (MuSK-MG)
Myasthenia gravis (MG) is a rare, debilitating, autoimmune disease that affects the neuromuscular junction—the place where nerve cells and muscle cells communicate. In MG, the body attacks special receptors on nerve cells that are sensitive to an important chemical called acetylcholine (ACh). ACh is an important chemical because it helps send messages from nerves across the neuromuscular junction to muscles, where these special receptors interpret the message. These special receptors are called acetylcholine receptors (AChR).1
There is a second chemical that is needed for proper nerve-muscle communication and it is called muscle-specific kinase (MuSK). MuSK also helps nerve-muscle communication across the neuromuscular junction. Unlike AChR-MG, in which the body attacks the receptor, in patients with MuSK-MG, their bodies attack cells that produce the MuSK chemical. It’s estimated that up to 8% of all people with MG have the MuSK-MG type.1,2
Symptoms3,4
Many symptoms of MuSK-MG are similar to AChR-MG, including:
- Weakness in the arms, hands, fingers, legs, and neck
- Change in facial expression
- Difficulty swallowing
- Shortness of breath
- Impaired speech
- Drooping of one or both eyelids
- Blurred or double vision due to weakness of the muscles that control eye movements
MuSK-MG affects females more often than males, has an earlier age of onset than AChR-MG, and a more severe disease course. It impacts facial/cranial nerves to a greater degree than AChR-MG, resulting in:
- Swallowing difficulties
- Chewing difficulties
- Slurred speech
- Drooling
- Choking on liquids
- Speech problems
Diagnosis2,3
Traditionally, corticosteroids and immunosuppressant’s are used to treat MG; other treatments include:
- Anticholinesterase inhibitors
- Plasmapheresis
- Immunoglobulin therapy
- Thymectomy
MuSK-MG is significantly resistant to treatment. In these patients, the search for alternative treatment strategies targeting different pathophysiologic aspects of the disease is a medical need.
Before initiating any therapy, patients with MuSK-MG should consult with a board-certified neurologist who specializes in neuromuscular diseases.
References:
- Koneczny I, Cossins J, Vincent A. The role of muscle-specific tyrosine kinase (MuSK) and mystery of MuSK myasthenia gravis. J Anat. 2014;224(1):29-35.
- El-Salem K, Yassin A, Al-Hayk K. et al. Treatment of MuSK-associated myasthenia gravis.Curr Treat Options Neurol. 2014;16(4):283.
- Pasnoor M, Wolfe GI, Nations S, et al. Clinical findings in MuSK-antibody positive myasthenia gravis: a US experience. Muscle Nerve. 2010;41(3):370-374.
- National Institute of Neurological Disorders and Stroke. Myasthenia gravis fact sheet. https://www.ninds.nih.gov/Disorders/Patient-Caregiver-Education/Fact-Sheets/Myasthenia-Gravis-Fact-Sheet
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