Myasthenia gravis classification

Myasthenia gravis may be classified into 4 sub types based on presence of autoantibodies: Pure ocular form, generalized form with anti-AChR antibodies, the forms without classical anti-AChR antibodies, neonatal MG, congenital.

Myasthenia gravis may be classified into 4 sub types based on presence of autoantibodies.

• 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.^[1]

About 85 percent of MG patients develop generalized disease with autoantibody against AchR.^[2] These antibodies are IgG1 and IgG3 subclasses which can bind to complement.^[3] Thymic abnormalities are more common in this group, especially thymic follicular hyperplasia.^[4] 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.^[5][6]
• These patients can have other autoimmune diseases like Hashimoto’s disease.^[7]
• Late onset myasthenia gravis (onset of the disease after the age of 50 (LOMG)): Patients with this type of the disease can present with thymoma, a tumor of thymic epithelial cells.^[8] In almost 50 percent of them we can find other antibodies like anti-ryanodine antibody, anti-titin antibody and anti-striated muscle antibody.^[9] most of the patients in this group have severe symptoms like bulbar involvement.^[10]

This subtype can be further divided into 3 groups

• The form with anti-anti-MuSK antibodies: About 5 percent of MG patients, especially females has this antibody which belongs to IgG4 subclasses and cannot bind to complement.^[11][12] their symptoms are mostly sever and involves facial, bulbar and respiratory muscles but spares ocular and thymic abnormalities.^[11][13] In these patients both presynaptic and postsynaptic components of NMJ are affected and the severity of the disease is related to the amount of antibodies.^[14][15]
• The form with anti-LRP4 antibodies: About 12-50 percent of patients who seems to be seronegative for anti-AchR and MuSK, presents antibody against LRP4.^[16][17][18]
• The form with clustered AChR antibodies: 5 percent of patients with MG doesn’t have any antibodies but in 50 percent of them we can see clustered AchR with cell assay detection.^[1]

• 10-20 percent of mothers with MG may have infants who display a transient neonatal myasthenia (TNM) for few days to 3 months.
• The cause of this condition is passive transfer of antibodies to the neonate.^[19]

• Congenital form of MG follows the Mendelian pattern and is caused by an error in the genes which are expressed in the NMJ.^[20]

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