What are the muscle weakness symptoms of 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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Rarely, patients with MG may present with respiratory muscle weakness without other prominent MG symptoms. [34] However, the vast majority of patients with respiratory muscle weakness have ocular and bulbar symptoms. Patients with diaphragmatic weakness will often have orthopnea as an early symptom. This may lead to respiratory compromise when the patient lies supine. Patients with MG and respiratory muscle weakness may report an inability to draw a full breath. They often describe their breathing as rapid and shallow, which may be misinterpreted as hyperventilation due to anxiety.

Fatigable extremity weakness in MG may affect any muscle group. Generally, it is proximal and often has an asymmetrical appearance. Characteristically, muscles are noted to weaken with repeated use, and strength improves with rest. Patients note difficulty getting up from chairs and going up and down the stairs. Patients may complain of a footdrop with prolonged walking, hip extension weakness with climbing several flights of stairs, shoulder muscle fatigue with activities that require holding their arms above their heads, and weakness of finger flexors and extensors with prolonged typing. Rarely, weakness may be very focal, affecting distal limb muscles or neck extensors selectively.

Pain, as a result of muscle aches or cramps, is commonly reported, especially in the neck. Sensory complaints are not a feature of MG; however, many patients get ulnar mononeuropathy at the elbow due to the constant attempts to hold the head up due to weakness of neck muscles.

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