Myasthenia gravis classification

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Charmaine Patel, M.D. [2]

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Classification

Myasthenia gravis may be classified into 3 subtypes based on presence of autoantibodies.

Pure ocular form

Ocular symptoms are the initial symptom in most of the MG cases. In about 15 percent of these patients this initial symptom will not progress to generalized disease after 2 years and they will classify as pure ocular form of the Myasthenia gravis. In approximately 50 percent of these patients we can’t detect antibodies by classical assay and we need to detect them through cell-based assay.

Generalized form with anti-AChR antibodies

About 85 percent of MG patients develop generalized disease with autoantibody against AchR.(31) These antibodies are IgG1 and IgG3 subclasses which can bind to complement.(33) Thymic abnormalities are more common in this group, especially thymic follicular hyperplasia.(32) this subtype can be further divided into 2 groups:

• Early onset myasthenia gravis (onset of the disease before the age of 50 (EOMG)): In this group we have female predominance with the ratio of 3/1. Thymic follicular hyperplasia is more common in this group and is believed to be related to deregulation of sex hormones and their receptors on thymic cells. (34-35)These patients can have other autoimmune diseases like Hashimoto’s disease.(36)
• Late onset myasthenia gravis (onset of the disease after the age of 50 (LOMG)):

The forms without classical anti-AChR antibodies

• The form with anti-anti-MuSK antibodies
• The form with anti-LRP4 antibodies
• The form with clustered AChR antibodies