Myasthenia Gravis Overview Myasthenia Gravis is an autoimmune disorder of the postsynaptic neuromuscular junction. Ab to AChR blocks receptor function, resulting in diminished muscle contraction. Associated with: - Thymic tumors - Paraneoplastic effects of SCC or Hodgkin lymphoma - Autoimmune: thyroid, Sjogren syndrome, rheumatoid arthritis, SLE Myasthenia Epidemiology: - Bimodal age distribution in the 30s (female predominance) and 60s-70s (male predominance). Clinical Picture of Myasthenia Gravis: - Fatiguability: Worse towards the end of the day - Fluctuating degree/variable degree of weakness in: 1. Ocular- 50%: Ptosis, diplopia 2. Bulbar- 15%: Dysphagia, dysarthria, hypophonia, fatiguable chewing, loss of smile 3. Neck: “dropping head syndrome” 4. Limb- proximal weakness, arms > legs 5. Respiratory muscles: “myasthenic crises”. Respiratory insufficiency and life-threatening Differential DX: - Thyroid ophthalmopathy - Kearns-Sayre syndrome - Myotonic dystrophy - Brain stem/Cranial nerve pathology - Generalized fatigue - ALS - Lambert Eaton myasthenia syndrome - Miller Fischer and PCB variants of GBS - Botulism - Penicillamine induced myasthenia Diagnosis - Clinical, Serologic and EMG Findings: 1. Clinical DX: - Bedside: ice pack test/Edrophonium test - Cogan sign - Peek sign 2. Imaging - CT Chest: Evaluate for thymoma 3. Electrophysiologic Confirmation: - Repetitive nerve stimulation - Single fiber electromyography 4. Labs: - AchR antibodies: first step in immunologic assay - MuSK antibodies - LRP4 antibodies Myasthenia Gravis Treatment: - Symptomatic Treatment: acetylcholinesterase inhibition - Chronic Immunosuppressive Therapies: Steroids and NSAIDs - Immunomodulating Treatments: IVIG and Therapeutic plasma exchange - Surgical Treatment: Thymectomy Myasthenia Crises - Severe bulbar weakness: - Dysphagia and aspiration and acute respiratory failure - Can be precipitated by: Drugs, infection, surgery, childbirth, tapering of immunosuppressants - Meds to Avoid: Fluoroquinolones, Magnesium, Anesthetics, Penicillamine, Beta blockers, Procainamide #Myasthenia #Gravis #diagnosis #management #neurology
