Snapshot A 62-year-old man presents to his primary care physician for "seeing double." He reports that he has been experiencing these symptoms for a few months. His diplopia is worse after reading a book or watching television. He says that at times he notices his left eyelid "droops" at the end of the day and improves after waking up from sleep. He notes episodes of fluctuating weakness when chewing harder foods. On physical examination, there is left-sided ptosis. Pupillary reflex is intact. A plastic glove with ice is applied on the ptosis for approximately 2 minutes and the ptosis markedly improves. Serology is positive for anti-acetylcholine receptor antibodies and preparations are made for a computerized tomography scan of the chest. Introduction Clinical definition autoimmune disorder of the neuromuscular junction Associated conditions thymoma thymic hyperplasia Epidemiology Incidence has a bimodal distribution more common in younger women (< 40 years of age) and older men (> 50 years of age) Risk factors HLA-B8 medications penicillamine aminoglycosides Pathogenesis Autoantibodies directed against a protein of the neuromuscular junction autoantibodies can be directed against nicotinic acetlycholine receptor (AChR) login to view 1 more bullet muscle-specific receptor tyrosine kinase (MuSK) categorized as a type II hypersensitivity reaction T-cells play a role as well thought to stimulate B-cell antibody production Presentation Symptoms general feature fluctuating muscle weakness login to view 2 more bullets true muscle fatigue login to view 1 more bullet ocular symptoms most common presenting symptoms login to view 2 more bullets bulbar symptoms dysphagia dysarthria fatigable chewing proximal muscle weakness Physical exam ice-pack test place ice on the patient's ptosis → ptosis improves login to view 2 more bullets edrophonium chloride (Tensilon test) only used in patients with ptosis or ophthalmoparesis login to view 1 more bullet edrophonium is an acetylcholinesterase inhibitor that has a short duration of action login to view 1 more bullet may result in false positives or cause life threatening bradycardia; thus, this test is rarely performed Imaging Computerized tomography (CT) scan indication to rule out a thymoma view chest Studies Labs serologic testing for autoantibodies anti-AChR login to view 1 more bullet anti-MuSK Electromyogram (EMG) decremental decrease in the compound muscle action potential (CMAP) Differential Lambert-Eaton myasthenic syndrome (LEMS) differentiating factor muscle weakness that improves with use autonomic manifestations Botulism differentiating factor poor or impaired pupillary response to light Thyroid ophthalmopathy Treatment Medical corticosteroids indication login to view 1 more bullet drugs login to view 1 more bullet acetylcholinesterase inhibitors indication login to view 1 more bullet drugs login to view 1 more bullet adverse effects login to view 4 more bullets Procedural intravenous immunoglobulins (IVIg) or plasmapheresis indication login to view 1 more bullet Surgical thymectomy indication login to view 2 more bullets Complications Myasthenic crisis respiratory weakness secondary to myasthenia gravis Prognosis Most patients with ocular involvement progress to generalized myasthenia gravis