Diagnosis of Myasthenia Gravis

Educational Objectives

The goal of this program is to improve diagnosis and treatment of ophthalmologic diseases. After hearing and assimilating this program, the clinician will be better able to:

1. Distinguish between thyroid eye disease and myasthenia gravis.

Summary

Diagnosis: myasthenia gravis (MG) should be considered in patient with ptosis or diplopia; clinician should assess variability of symptoms; patients may report diplopia or changes in position of lids; most patients feel worse at end of day, so this symptom too common to be helpful; symptoms may be episodic; antibodies to acetylcholine receptor (AChR) may be seen in patient with no complaints and normal examination

Differential diagnosis: in patients with thyroid eye disease, symptoms of diplopia worsen after nap because of congestion of orbit associated with supine position; in contrast, patients with MG improve after rest; like syphilis and sarcoidosis, MG has protean manifestations; when cranial nerve III (CN3), CN4, and CN6 involved on same side, imaging needed to rule out meningioma of cavernous sinus; brainstem pattern, internuclear ophthalmoplegia (INO), pseudo-INO, or gaze palsy may be present; bilateral INO may be caused by stroke, multiple sclerosis, or MG

Tests for MG: helpful findings on examination include Cogan lid twitch, fast saccades, quiver eye movements, and weakness of orbicularis oculi; curtain sign of enhanced ptosis not unique to MG; Cogan lid twitch — brief hop elicited when patient looks down for 10 to 20 seconds, then gazes straight ahead; repetition may demonstrate characteristic fatigue; rapid saccades — seen with quiver of eyes; quiver eye movements signify MG but fatigue quickly; patient should be re-examined after resting; lids — in normal patient, examiner cannot manually open lids with 2 fingers when patient asked to keep them closed; rest test — if lid lifts ≥2 mm more after rest, compared with baseline, MG suspected; ice test — alternative to rest test; ice held on one lid for ≈2 min to look for improvement; test uncomfortable for patient; sleep test — assesses motility and ptosis over 30 min; bilateral improvements in motility and ptosis indicate MG

Antibodies: in literature, antibodies to AChR reported in 30% to 50% of patients with MG; however, in speaker’s study of 223 patients, antibodies found in 71% of cases; test for antibodies less likely to be positive in women; results vary, so test should be repeated; testing for antibodies to muscle-specific kinase expensive and only positive in few cases of pure ocular MG; electromyography (EMG) detects 50% of cases; single-fiber EMG detects 95% of cases of ocular MG but test takes ≈2 hr and not widely available

Prognosis: in speaker’s study of 158 patients, 21% of those with ocular MG had generalized MG; higher levels of antibodies associated with higher risk for generalized disease

Readings

Nagia L et al: Prognosis of ocular myasthenia gravis: retrospective multicenter analysis. Ophthalmology 2015 Jul;122(7):1517-21; Peeler CE et al: Clinical utility of acetylcholine receptor antibody testing in ocular myasthenia gravis. JAMA Neurol 2015 Oct;72(10):1170-4; Smith SV, Lee AG: Update on ocular myasthenia gravis. Neurol Clin 2017 Feb;35(1):115-123.

Disclosures

For this program, members of the faculty and planning committee reported nothing to disclose.

Acknowledgements

Dr Cornblath was recorded at Current Concepts of Ophthalmology 2018, presented by the NYU School of Medicine and held January 5-6, 2018, in Atlantic City, NJ. To learn about CME activities from the NYU School of Medicine, please visit med.nyu.edu. The Audio Digest Foundation thanks the speakers and the NYU School of Medicine for their cooperation in the production of this program.

CME/CE INFO

Accreditation:

The Audio- Digest Foundation is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education for physicians.

The Audio- Digest Foundation designates this enduring material for a maximum of 0 AMA PRA Category 1 Credits™. Physicians should claim only the credit commensurate with the extent of their participation in the activity.

Audio Digest Foundation is accredited as a provider of continuing nursing education by the American Nurses Credentialing Center's (ANCC's) Commission on Accreditation. Audio Digest Foundation designates this activity for 0 CE contact hours.

Lecture ID:

OP560803

Expiration:

This CME course qualifies for AMA PRA Category 1 Credits™ for 3 years from the date of publication.

Instructions:

To earn CME/CE credit for this course, you must complete all the following components in the order recommended: (1) Review introductory course content, including Educational Objectives and Faculty/Planner Disclosures; (2) Listen to the audio program and review accompanying learning materials; (3) Complete posttest (only after completing Step 2) and earn a passing score of at least 80%. Taking the course Pretest and completing the Evaluation Survey are strongly recommended (but not mandatory) components of completing this CME/CE course.

Estimated time to complete this CME/CE course:

Approximately 2x the length of the recorded lecture to account for time spent studying accompanying learning materials and completing tests.