9.17 - SECTION 3The Efferent Visual SystemDisorders of the Neuromuscular Junction

Abstract

Neuromuscular junction disorders are caused by an antibody-mediated autoimmune attack on postsynaptic acetylcholine (ACh) receptors or the altered presynaptic release of acetylcholine. Myasthenia gravis (MG) is the most common disorder of the neuromuscular junction. The diagnosis of MG is usually based on history and physical examination. A combination of physical examination, pharmacological tests, blood tests, and electrodiagnostic tests may be needed to confirm the diagnosis. A serum assay for anti-ACh receptor antibodies should be obtained for all patients who have suspected MG. Seronegative patients comprise 10%–15% of those with MG. Electrophysiological tests are useful for the diagnosis of MG when other tests are inconclusive. Chest imaging is mandatory as 10-15% of MG patients have a thymic tumor. Pyridostigmine, an acetylcholinesterase inhibitor, is often used in the treatment of myasthenia because of its safety profile. Thymectomy is indicated for patients who have a thymoma. Thymectomy may be considered in seronegative or ocular MG if the disease is refractory to standard immunotherapy. Immunosuppressants, mainly cytotoxic agents and corticosteroids, treat the disease directly and are generally used either to prevent the progression of ocular to generalized MG or employed in patients who do not improve satisfactorily with acetylcholinesterase inhibitors. Botulism and Lambert–Eaton myasthenic syndrome are other disorders of neuromuscular junction discussed in this chapter.