PAGE CONTENTS

Clinical Features

Myasthenia gravis (MG) is a rare autoimmune disease affecting the neuromuscular junction (NMJ). Immune system autoantibodies attack components of the NMJ, delaying the transmission of signals from nerves to post-synaptic motor endplates in muscle tissue.

The hallmark clinical feature of MG is fluctuating weakness and fatigue in voluntary skeletal muscles that increase with repetitive movements and are relieved by rest. The weakness especially affects the ocular, bulbar, facial, neck, limb, and respiratory musculature.¹

Ocular Clinical Presentation

Approximately 15% of patients have purely ocular MG, in which only the external ocular muscles such as the levator palpebrae are affected. Recognizable symptoms include ptosis (drooping eyelids) and diplopia (double vision). Ptosis and diplopia fluctuate in severity and may worsen throughout the day.²

Specific clinical tests for ocular symptoms include the following³:

Sustained upward gaze for 60 to 180 seconds causes ptosis.
Sustained lateral gaze for 60 seconds triggers diplopia.
Sustained tight closure of the eyelids tires the orbicularis oculi muscles; the “peek sign,” in which the white sclera is seen through a partially open eyelid, develops slowly.
Manual elevation of the more ptotic eyelid may exacerbate ptosis in the contralateral lid (enhanced ptosis).

Ocular signs and symptoms are typically present in approximately 75% of individuals with MG and are most frequently observed initially.⁴

In most cases, ocular MG progresses to generalized MG, which peaks within the first 2 to 3 years after symptom onset. In generalized MG, weakness and fatigue affect muscles other than the eye muscles.²

Bulbar/Facial/Respiratory Clinical Presentation

When the bulbar musculature is affected, a patient with MG has difficulty chewing, swallowing (dysphagia), and speaking (dysarthria).⁴ Weakness in the facial and neck muscles affects facial expression and the ability to hold up the head. Facial muscle weakness causes patients to appear tired or sad. Weakness in the respiratory muscles interferes with breathing and sustained speech.⁴

Clinical tests for bulbar and respiratory systems include the following³:

Prolonged phonation of the sound “eeeeeee” at a high pitch;
Counting aloud from 1 to 50 with breathing allowed, or counting aloud from 1 to 20 with only a single breath allowed at the beginning.

The development of vocal hoarseness, shortness of breath, or dysarthria during these tests indicates weakness and fatigability of the laryngeal or respiratory muscles.³ The patient may report greater difficulty swallowing liquids than solid foods; swallowing liquids may provoke aspiration, coughing, choking, throat clearing, or nasal regurgitation of fluids.⁴ To assess the extent to which bulbar dysfunction is causing aspiration, the patient should be referred for an official barium swallow study with videofluoroscopy.⁵ Even more MG-specific is a fiberoptic endoscopic evaluation of swallowing with concurrent edrophonium (Tensilon) application (FEES-Tensilon test).⁶

Generalized Extremity Clinical Presentation

Patients with generalized MG may exhibit weakness in the muscles of the extremities, especially those surrounding the joints closest to the torso (shoulders and hips).⁴ Clinical tests to assess extremity strength and endurance include the following³:

Sustained arm abduction (or flexion) at shoulder height for at least 120 seconds;
Sustained leg elevation for 90 seconds while lying supine;
Repeated sit-to-stands from a chair without arm use for up to as many as 20 repetitions;
Repeated double leg squats during palm-to-palm contact with the clinician.

Muscle fatigue and weakness quickly develop during repeated muscle contractions, such as those necessary to sustain positioning against gravity, or during repeated movements like squats and sit-to-stands. The patient either fails to maintain arm or leg positions or demonstrates considerable weakness if the clinician manually tests muscle strength following prolonged holds. Signs of early weakness with sit-to-stands include leaning forward, trying to use the arms, and scooting forward with the buttocks on the chair. Any increased pressure against the clinician’s palms during double leg squats indicates early weakness.³

Patients with MG may report experiencing fatigue or weakness, particularly following bouts of intense activity (exercise) or at the end of the day.⁴

References

Bird SJ. Clinical manifestations of myasthenia gravis. UpToDate. Accessed February 18, 2022.
Melzer N, Ruck T, Fuhr P, et al. Clinical features, pathogenesis, and treatment of myasthenia gravis: a supplement to the Guidelines of the German Neurological Society. J Neurol. 2016;263:1473-1494. doi:10.1007/s00415-016-8045-z
Jowkar AA. Which maneuvers should be included in the physical exam of suspected myasthenia gravis (MG)? Medscape. Accessed February 17, 2022.
Jowkar AA. Myasthenia gravis clinical presentation. Medscape. Updated August 27, 2018. Accessed February 18, 2022.
Higo R, Nito T, Tayama N. Videofluoroscopic assessment of swallowing function in patients with myasthenia gravis. J Neurol Sci. 2005;231(1-2):45-48. doi:10.1016/j.jns.2004.12.007
Warnecke T, Teismann I, Zimmermann J, Oelenberg S, Ringelstein EB, Dziewas R. Fiberoptic endoscopic evaluation of swallowing with simultaneous Tensilon application in diagnosis and therapy of myasthenia gravis. J Neurol. 2008;255(2):224-230. doi:10.1007/s00415-008-0664-6

Reviewed by Harshi Dhingra, MD, on 2/22/2022.

Maria Arini Lopez, PT, DPT, CSCS, CMTPT, CIMT

Maria Arini Lopez, PT, DPT, CSCS, CMTPT, CIMT is a freelance medical writer and Doctor of Physical Therapy from Maryland. She has expertise in the therapeutic areas of orthopedics, neurology, chronic pain, gastrointestinal dysfunctions, and rare diseases especially Ehlers Danlos Syndrome.

Myasthenia Gravis