Snapshot A 42-year-old woman presents to her primary care physician for fatigue. She reports that her fatigue is worse towards the end of the day. She also notes that while bathing her nephew in the shower her head would "drop." At times when she is watching television or reading a book she sees double. Lastly, she would see her left or right eyelid droop after returning from work. On physical exam, there is right-sided ptosis after sustaining upward gaze for a few minutes. A tensilon test is performed, which is demonstrated in the clinical image below. Serologic studies return positive for anti-acetylcholine receptor antibodies. Preparations are made to have a computerized tomography scan of the chest. Introduction Clinical definition autoimmune disorder of the neuromuscular junction Epidemiology incidence has a bimodal distribution login to view 1 more bullet risk factors HLA-B8 medications login to view 2 more bullets Pathogenesis autoantibodies directed against a protein of the neuromuscular junction autoantibodies can be directed against login to view 3 more bullets categorized as a type II hypersensitivity reaction T-cells play a role as well thought to stimulate B-cell antibody production Associated conditions thymoma thymic hyperplasia Prognosis most patients with ocular involvement progress to generalized myasthenia gravis 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 can also be used to monitor treatment with pyridostigmine login to view 2 more bullets 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 plasmapharesis indication login to view 1 more bullet Surgical thymectomy indication login to view 1 more bullet Complications Myasthenic crisis respiratory weakness secondary to myasthenia gravis Increased sensitivity to non-depolarizing acetylcholine receptor blockers such as vecuronium