Diagnosis of myasthenia gravis
- Shawn J Bird, MD
Shawn J Bird, MD
- Professor of Neurology
- University of Pennsylvania School of Medicine
- Section Editors
- Jeremy M Shefner, MD, PhD
Jeremy M Shefner, MD, PhD
- Section Editor — Neuromuscular Disease
- Professor and Chair of Neurology, Barrow Neurological Institute
- Professor of Neurology, University of Arizona, Phoenix
- Clinical Professor of Neurology, Creighton University
- Ira N Targoff, MD
Ira N Targoff, MD
- Section Editor — Muscle Disease
- Professor of Medicine, Section of Rheumatology
- University of Oklahoma Health Sciences Center
Myasthenia gravis is the most common disorder of neuromuscular transmission. It is now one of the best characterized and understood autoimmune disorders. The hallmark of the disorder is a fluctuating degree and variable combination of weakness in ocular, bulbar, limb, and respiratory muscles. Weakness is the result of an antibody-mediated, T-cell dependent immunologic attack directed at proteins in the postsynaptic membrane of the neuromuscular junction (acetylcholine receptors or receptor-associated proteins). The diagnosis of myasthenia gravis can be established by clinical and serologic testing [1,2].
This topic will discuss the diagnosis of myasthenia gravis. Other aspects of this disorder are discussed separately. (See "Pathogenesis of myasthenia gravis" and "Clinical manifestations of myasthenia gravis" and "Differential diagnosis of myasthenia gravis" and "Treatment of myasthenia gravis".)
The diagnostic approach to myasthenia is focused on confirming the clinical diagnosis established by the history and typical examination findings. (See "Clinical manifestations of myasthenia gravis".)
Bedside tests (the edrophonium test and the ice pack test) are easy to perform and are sensitive, but they have major limitations due to concerns about excess false-positive results. Confirmation by these tests alone is unwise.
More reliable laboratory methods that aid in the confirmation are serologic tests for autoantibodies and electrophysiologic studies (repetitive nerve stimulation studies and single-fiber electromyography [EMG]). It should be kept in mind that the diagnostic sensitivity of these studies also varies considerably depending on whether the patient has ocular or generalized disease.
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- DIAGNOSTIC APPROACH
- BEDSIDE TESTS
- Ice pack test
- Edrophonium test
- SEROLOGIC TESTING
- Acetylcholine receptor antibodies
- MuSK antibodies
- - Clinical features
- Seronegative myasthenia
- Other antibodies
- ELECTROPHYSIOLOGIC CONFIRMATION
- Repetitive nerve stimulation
- Single-fiber electromyography
- ASSOCIATED CONDITIONS
- Thymic tumors and other malignancies
- Autoimmune disorders
- DIFFERENTIAL DIAGNOSIS
- INFORMATION FOR PATIENTS
- SUMMARY AND RECOMMENDATIONS