Differential 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 (MG) is the most common disorder of neuromuscular transmission. 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 immunological attack directed at proteins in the postsynaptic membrane of the neuromuscular junction (acetylcholine receptors or receptor-associated proteins). The diagnosis of MG can be established by clinical and serologic testing [1,2].
This topic will discuss the differential diagnosis of MG, including conditions that mimic ocular myasthenia and conditions that mimic generalized myasthenia. The diagnosis of MG is discussed separately, as are other aspects of this disorder. (See "Diagnosis of myasthenia gravis" and "Clinical manifestations of myasthenia gravis" and "Pathogenesis of myasthenia gravis" and "Treatment of myasthenia gravis".)
DIAGNOSIS OF MYASTHENIA GRAVIS
The diagnosis of MG is reviewed here briefly and discussed in detail elsewhere. (See "Diagnosis of myasthenia gravis".)
The optimal approach to the diagnosis of myasthenia gravis varies with the clinical setting. The first step is to establish that the symptoms and signs are consistent with myasthenia gravis and not another disorder. (See "Clinical manifestations of myasthenia gravis".)
The bedside ice pack test can be used to support the diagnosis of myasthenia gravis in patients with ptosis, but it is not helpful for those with extraocular muscle weakness. The edrophonium (Tensilon) test should be used only in those patients with obvious ptosis or ophthalmoparesis, in whom improvement after infusion of the drug can easily be observed. The sensitivity of the Tensilon test for the diagnosis of MG is in the range of 80 to 90 percent, but it is associated with many false-negative and false-positive results. (See "Diagnosis of myasthenia gravis", section on 'Bedside tests'.)
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- DIAGNOSIS OF MYASTHENIA GRAVIS
- DIFFERENTIAL BY PRESENTATION
- CONDITIONS THAT MIMIC OCULAR MYASTHENIA
- CONDITIONS THAT MIMIC GENERALIZED MYASTHENIA
- Generalized fatigue
- Motor neuron disease
- Lambert-Eaton myasthenic syndrome
- Penicillamine-induced myasthenia
- Statins and myasthenia
- Congenital myasthenic syndromes