Myasthenia Gravis

Myasthenia gravis (MG) is an autoimmune disease associated with the presence of autoantibodies directed against the acetylcholine receptor (AChRAB) and muscle-specific kinase (MuSK).

These antibodies are etiopathogenic and associated with dysfunction of the neuromuscular junction, which is responsible for severe muscle weakness in major muscle groups.

Antibody testing is necessary to confirm the diagnosis of autoimmune MG and for monitoring and ruling out other conditions. The prognosis may be guarded, but treatment is available. Early diagnosis is essential.

MG can occur from childhood through adulthood. In women, it is most prevalent between the ages of 20 and 30, and in men, it occurs in those over 50.

Antibodies in Myasthenia Gravis

• Anti-acetylcholine receptor (AChRAB)
• Anti-muscle-specific kinase (MuSK)
• Anti-titin (LOMG) (striated muscle)
• Anti-RyR (LOMG) (striated muscle)
• Anti-IL-12 and INF-δ (LOMG and Thymoma)
• Anti-VGKC (LGI1, CASPR2)

(Peripheral nerve hyperexcitability syndrome, peripheral neuromyotonia, and may coexist with AChRAB in MG with thymoma)

Anti-Acetylcholine Receptor Antibody (AChRAB)

• AChRAB testing is highly specific for the diagnosis and monitoring of MG.
• Approximately 90% of patients with acquired MG have detectable AChRAB levels.
• Their absence does not rule out the diagnosis. In such cases, an EMG is recommended
• In patients with ocular MG, AChRAB is present in about 60% of cases
• AChRAB is not present in genetic forms of MG (5–10%)
• AChRABs may be found in first-degree relatives of patients with MG; however, the presence of AChRABs without clinical symptoms is rare.

MG SUBGROUPS WITH AChRABs

• Early-Onset MG (EOMG)
• Maternal MG (MMG)
• Childhood/Juvenile MG (C/JMG)
• Late-Onset MG (LOMG)
• MG-Associated Thymoma (TAMG)

Seronegative MG (SNMG)

AChRAB-Seronegative MG

• MuSK+ MG: Female, young patients, HLA-DR14; -DQ5; generalized and very severe disease; absence of anti-titin and anti-RyR
• Low-affinity AChRAB+ MG (IgG1)
• 5–10% of patients with MG are seronegative for AChRAB, MuSK, anti-titin, anti-RyR, and anti-cytokines

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