How is jaw muscle weakness characterized in myasthenia gravis (MG)?

Updated: Aug 27, 2018
  • Author: Abbas A Jowkar, MBBS; Chief Editor: Nicholas Lorenzo, MD, CPE, MHCM, FAAPL  more...
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Patients with MG who have difficulty chewing may demonstrate weakness of jaw closure due to masseter and temporalis muscle weakness. Weakness of jaw opening due to pterygoid muscle weakness, on the other hand, is rarely seen. This pattern of weak jaw closure and relatively strong jaw opening is quite typical of MG. A frequent sign of jaw weakness is that the patient holds the jaw closed with the thumb under the chin, the index finger extended up the cheek, the middle finger curled under the nose and across the philtrum, producing a studious or attentive appearance. Typically, neck flexion is weaker than neck extension in patients with MG, although occasionally patients will present with a head-drop and have severe neck extension weakness.

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