Myasthenia gravis (MG) is an autoimmune disorder characterized by fluctuating muscle weakness and fatigue caused by antibodies directed against the nicotine acetylcholine (ACh) receptor (AChR) or against the muscle-specific tyrosine kinase (MuSK) receptor. The prevalence has increased over the past four to five decades, and the increase is mainly found in patients over the age of 50 years. Clinically and epidemiologically, it is possible to recognize two subtypes, the early-onset myasthenia gravis (EOMG) and the late-onset myasthenia gravis (LOMG). In MG, antibodies to the AChR cause a functional blockade of the binding site for ACh. Some MG patients do not have detectable AChR antibodies and are termed seronegative MG. In 2–3% of AChR-seronegative patients, there was seropositivity of anti-MuSK antibody. It had been reported that anti-AChR antibodies were seen in 65% with early-onset MG compared to 85% in the late-onset MG and elevated titers of anti-MuSK antibodies were similar. Ocular MG is more common in LOMG compared to EOMG so is myopathy. About 30% of late-onset MG patients without thymoma have antibodies to titin, whereas titin antibodies are uncommon in the early-onset MG. Significant therapeutic progress has been made in the treatment of MG and introduction of new modalities especially immunosuppressive, immunomodulating drugs, plasma exchange, and thymectomy. In Eaton-Lambert syndrome (E-LS), there is a reduction in the release of acetylcholine from the motor nerve terminals. There are substantial differences between E-LS and MG in the pathophysiology, clinical features, electromyographic changes, and treatment. More than half the patients with E-LS are associated with malignancies such as small cell lung cancer (SCLC) non-small cell lung cancer, and lymphoma, among others. The antibodies in E-LS prevent the opening of the calcium channels, and hence the release of ACh and voltage-gated calcium channels (VGCC) antibodies has been reported in 75–100% of patients with L-ES. Guanidine increases the release of ACh.
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