Updated: Dec 13, 2007
Myasthenia gravis (MG) is an autoimmune neuromuscular disease characterized by weakness and fatigue of the skeletal muscles of the face and extremities. It affects people of both sexes and all ages, but twice as many female patients are affected as male patients. MG usually strikes in women in their third decade of life.
The underlying pathology is the production of autoantibodies against human acetylcholine receptors (AChRs), usually immunoglobulin G, which can be detected in as many as 90% of patients. These antibodies interfere with the conduction of impulses across myoneural junctions by decreasing the number of available AChRs at neuromuscular junctions. Patients with milder symptoms tend to have lower antibody titers. Patients with thymoma and more severe disease have higher titers. Some MG patients may not have detectable antibody levels.
MG typically affects females during their reproductive years. Difficulties specific to pregnant patients can be concerning, and the course of MG during pregnancy is hard to predict. Patients may have disease exacerbation, crisis, or, interestingly enough, remission. Although the disease course is variable, pregnant patients face risks of exacerbation, respiratory failure, adverse drug response, crisis, and death.
Mitchell and Bebbington reviewed the performance of MG patients during pregnancy at the Vancouver Salvation Army Grace Hospital. Four of 9 patients experienced antepartum exacerbations ranging from muscle weakness to respiratory failure. Three of the 4 patients had undergone previous thymectomy, and the patient with the worst symptoms (respiratory failure) had a prior thymectomy.1 These findings negate studies that concluded that thymectomy leads to fewer exacerbations.
In a large study from 1991, Plauche found that exacerbations occurred in approximately 41% of patients during pregnancy and in 29.8% of patients postpartum. Approximately 4% of patients died because of worsening of the disease or because of treatment complications.2
A study by Batocchi et al reported that the disease worsened in 10 (19%) of 54 patients. Approximately 60% of exacerbations occurred during the first trimester, and approximately 28% of patients deteriorated immediately after delivery. Premature delivery occurred in 4 (7.4%) of 54 patients. Cesarean delivery was performed in 16 pregnancies (30%). The study concluded that no correlation exists between MG severity before and during pregnancy.3
Worldwide prevalence is approximately 40 cases per million population, and the incidence is 1 case in 20,000-40,000 population per year.
Persons of all races are affected.
Both sexes are affected, and the female-to-male ratio is 2:1.
Persons of any age are affected, but MG usually affects women in their third decade of life.
Patients with myasthenia gravis present with symptoms such as ptosis, diplopia, breathing and swallowing difficulties, and weak limbs. Intermittent ptosis and diplopia are usually the initial reported symptoms. Symptoms usually become generalized within 1 year. Symptoms fluctuate in severity; they worsen with exertion and are relieved with rest. Fatigue upon exertion is essential to making the diagnosis. Despite these common presenting symptoms, some patients have atypical presentations.
Upon physical examination, muscle strength should be assessed by having the patient squeeze the examiner's hand repeatedly or having the patient flex her arm against resistance. Facial weakness can be evaluated by asking the patient to smile. A snarling expression may be evident when the patient attempts to smile. Although muscles are weak, deep tendon reflexes are preserved. Diplopia and ptosis should also be addressed.
The underlying pathology is the production of autoantibodies against human AChRs, usually immunoglobulin G, which can be detected in as many as 90% of patients.
The differential diagnosis of myasthenia gravis includes conditions associated with weakness of muscles, such as Lambert-Eaton myasthenic syndrome, botulism, hyperthyroidism, neurasthenia, intracranial mass lesion, progressive external ophthalmoplegia, and drug-induced MG.
Screen for other autoimmune disorders, including rheumatoid arthritis, systemic lupus erythematosus, pemphigus, Hashimoto thyroiditis, scleroderma, dermatitis herpetiformis, autoimmune hemolytic anemia, polymyositis, and sarcoidosis.
Obtain CT scans to study the thymus, or obtain MRIs to evaluate the mediastinum.
Rest is very important to restore muscle strength, especially during pregnancy.
Combination drug therapy is reported to be safer and more effective than monotherapy. Pharmaceutical treatment for myasthenia gravis (MG) is very effective.
Preferred treatment for MG and reportedly are safe in pregnancy. Increase the amount of acetylcholine available to bind to receptors. Neostigmine was the first drug used for MG.
Longer-acting cholinesterase inhibitor that can be used when edrophonium is ineffective. Inhibits destruction of acetylcholine by acetylcholinesterase, which facilitates transmission of impulses across myoneural junctions.
Although it has a short duration, activity is more pronounced.
Because of changed renal excretion rates and changed absorption of drugs, patients who are pregnant receive increased doses in increments of 5-10 mg. IM injection may eliminate these problems.
15 mg/dose PO q2-3h; not to exceed 375 mg/d
Not established
Atropine antagonizes muscarinic effects; effects of neuromuscular agents are increased
Documented hypersensitivity; GI or GU obstruction
C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus
Caution in epilepsy, asthma, bradycardia, hyperthyroidism, cardiac arrhythmia, or peptic ulcer; anticholinesterase insensitivity can develop for brief or prolonged periods
Acts in smooth muscle, CNS, and secretory glands. Blocks action of acetylcholine at parasympathetic sites and facilitates transmission of impulses across myoneural junctions.
Longer-acting medication that may last throughout night. Edrophonium test can be used with caution to find therapeutic doses.
Because of changed renal excretion rates and changed absorption of drugs, pregnant patients receive increased doses in increments of 15-30 mg. IM injection may eliminate these problems.
30 mg PO tid/qid; not to exceed 120 mg q4h
Not established
Increases effects of depolarizing neuromuscular blockers; increases toxicity of edrophonium
Documented hypersensitivity; GI or GU obstruction
C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus
Caution in bronchial asthma and persons receiving cardiac glycosides; overdose may cause cholinergic crisis, which may be fatal; have IV atropine readily available for treatment of cholinergic reactions; adverse muscarinic effects include flatulence, diarrhea, vomiting, abdominal cramps, and salivation
Immunosuppressants useful in treatment of MG. Deoxycorticosteroids (DOCs) for severely ill patients. Work by decreasing antibody synthesis and inhibiting CD4+ T-cell proliferation. Johns' regimen is the accepted regimen for steroid use in MG. Prednisone is fairly safe during pregnancy. Patients who wish to become pregnant are recommended to get pregnant while in steroid-induced remission. Cleft lip and palate in newborns of patients on steroids were noted in a few instances. High-dose corticosteroids can lead to premature rupture of membranes. Weight gain and cushingoid appearance are common complications.
Immunosuppressant for treatment of autoimmune disorders. May decrease inflammation by reversing increased capillary permeability and suppressing PMN activity. Stabilizes lysosomal membranes and also suppresses lymphocytes and antibody production.
Steroids cannot be discontinued because relapse will follow.
60-80 mg/d PO until improvement is observed; taper over 2 wk as symptoms resolve
Not established
Coadministration with estrogens may decrease clearance; concurrent use with digoxin may cause digitalis toxicity secondary to hypokalemia; phenobarbital, phenytoin, and rifampin may increase metabolism of glucocorticoids (consider increasing maintenance dose); monitor for hypokalemia with coadministration of diuretics
Documented hypersensitivity; viral infection; peptic ulcer disease; hepatic dysfunction; connective tissue infections; fungal or tubercular skin infections; GI disease
B - Fetal risk not confirmed in studies in humans but has been shown in some studies in animals
Abrupt discontinuation may cause adrenal crisis; hyperglycemia, edema, osteonecrosis, myopathy, peptic ulcer disease, hypokalemia, osteoporosis, euphoria, psychosis, MG, growth suppression, and infections may occur with glucocorticoid use
Azathioprine is used when response to corticosteroids is not adequate or when corticosteroid dosage must be decreased. Also, this drug added if symptoms are not controlled satisfactorily with acetylcholinesterase. It is converted to the metabolite mercaptopurine and inhibits T-cell reactivity. Azathioprine is found to reduce serum anti-AChR antibody titers. Cyclosporine is a strong immunosuppressant and inhibits T-cell activation. It is restricted to patients who do not respond well to other medications.
Antagonizes purine metabolism and inhibits synthesis of DNA, RNA, and protein. May decrease proliferation of immune cells, which results in lower autoimmune activity.
50 mg/d PO initially; may increase qwk to 3 mg/kg/d PO; eventually decrease to 1 mg/kg/d PO
Not established
Toxicity increases with allopurinol; concurrent use with ACE inhibitors may induce severe leukopenia; may increase levels of methotrexate metabolites and decrease effects of anticoagulants, neuromuscular blockers, and cyclosporine
Documented hypersensitivity; low levels of serum TPMT
D - Fetal risk shown in humans; use only if benefits outweigh risk to fetus
Increases risk of neoplasia; caution with liver disease and renal impairment; hematologic toxicities may occur; check TPMT level prior to therapy and follow liver, renal, and hematologic function; pancreatitis is rare; monitor CBC count and LFT results qwk for first month; can be used during pregnancy but with caution
Cyclic polypeptide that suppresses some humoral immunity and, to a greater extent, cell-mediated immune reactions such as delayed hypersensitivity, allograft rejection, experimental allergic encephalomyelitis, and graft versus host disease for a variety of organs.
For children and adults, base dosing on ideal body weight.
3 mg/kg/d PO initially; may increase to 5 mg/kg/d PO bid
Not established
Carbamazepine, phenytoin, isoniazid, rifampin, and phenobarbital may decrease cyclosporine concentrations; azithromycin, itraconazole, nicardipine, ketoconazole, fluconazole, erythromycin, verapamil, grapefruit juice, diltiazem, aminoglycosides, acyclovir, amphotericin B, and clarithromycin may increase cyclosporine toxicity; acute renal failure, rhabdomyolysis, myositis, and myalgias increase when taken concurrently with lovastatin
Documented hypersensitivity; uncontrolled hypertension or malignancies; do not administer concomitantly with PUVA or UVB radiation in psoriasis because may increase risk of cancer
C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus
Adverse effects include renal toxicity and hypertension, which are reversible with cessation of drug; evaluate renal and liver functions often by measuring BUN, serum creatinine, serum bilirubin, and liver enzymes; may increase risk of infection and lymphoma; reserve IV use only for those who cannot take PO
Useful in myasthenic crisis. Neutralize circulating myelin antibodies through antiidiotypic antibodies. Down-regulate proinflammatory cytokines (including INF-gamma), block Fc receptors on macrophages, suppress inducer T and B cells and augment suppressor T cells, block complement cascade, and promote remyelination.
Thought to interfere with anti-AChR antibodies. Improvement noticeable in 3-21 d and lasts as long as 3 mo.
0.4 g/kg/d IV over 5 d
Not established
Increases toxicity of live virus vaccine (MMR); do not administer within 3 mo of vaccine
Documented hypersensitivity; IgA deficiency; anti-IgE/IgG antibodies
C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus
Check serum IgA before IVIG (use an IgA-depleted product, eg, Gammagard S/D); infusions may increase serum viscosity and thromboembolic events; infusions may increase risk of migraine attacks, aseptic meningitis (10%), urticaria, pruritus, or petechiae (2-5 d postinfusion to 30 d); increases risk of renal tubular necrosis in elderly patients and those with diabetes, volume depletion, or preexisting kidney disease; laboratory test result changes associated with infusions include elevated antiviral or antibacterial antibody titers for 1 mo, 6-fold increase in ESR for 2-3 wk, and apparent hyponatremia
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MG, autoimmune neuromuscular disease, human acetylcholine receptors, AChRs, pregnancy complications, pregnancy comorbidity, autoimmune neuromuscular disease, rheumatoid arthritis, systemic lupus erythematosus, SLE, pemphigus, Hashimoto thyroiditis, Hashimoto's thyroiditis, thymic abnormality, scleroderma, dermatitis herpetiformis, autoimmune hemolytic anemia, polymyositis, sarcoidosis, MG and pregnancy
Idan Sharon, MD, Consulting Staff, Departments of Neurology and Psychiatry, Cornell New York Methodist Hospital; Private Practice
Idan Sharon, MD is a member of the following medical societies: American Academy of Neurology, American Medical Association, and Medical Society of the State of New York
Disclosure: Nothing to disclose.
Bryan D Cowan, MD, Professor and Chairman, Department of Obstetrics and Gynecology, University of Mississippi College of Medicine; Consulting Staff, Department of Obstetrics and Gynecology, Veterans Affairs Medical Center; Medical Director, Wiser Hospital for Women, University of Mississippi Medical Center
Bryan D Cowan, MD is a member of the following medical societies: American Association of Gynecologic Laparoscopists, American College of Obstetricians and Gynecologists, American Gynecological and Obstetrical Society, American Medical Association, American Society for Reproductive Medicine, Association of Professors of Gynecology and Obstetrics, Central Association of Obstetricians and Gynecologists, Endocrine Society, Sigma Xi, Society for Assisted Reproductive Technologies, Society for Gynecologic Investigation, Society for the Study of Reproduction, and Society of Laparoendoscopic Surgeons
Disclosure: Nothing to disclose.
Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: Nothing to disclose.
Gail F Whitman-Elia, MD, Professor, Department of Obstetrics and Gynecology, University of South Carolina School of Medicine
Gail F Whitman-Elia, MD is a member of the following medical societies: American Association of Clinical Endocrinologists, American College of Clinical Endocrinologists, American College of Obstetricians and Gynecologists, American Institute of Ultrasound in Medicine, American Medical Association, American Medical Women's Association, American Public Health Association, American Society for Reproductive Medicine, Endocrine Society, and South Carolina Medical Association
Disclosure: Nothing to disclose.
Frederick B Gaupp, MD, Consulting Staff, Department of Family Practice, Assumption Community Hospital
Frederick B Gaupp, MD is a member of the following medical societies: American Academy of Family Physicians
Disclosure: Nothing to disclose.
David Chelmow, MD, Professor of Obstetrics and Gynecology, Tufts University School of Medicine; Program Director, Tufts University Affiliated Hospitals OB/GYN Residency Program; Chair, Tufts University Health Sciences Campus Institutional Review Board
David Chelmow, MD is a member of the following medical societies: American College of Obstetricians and Gynecologists, American Medical Association, Association of Professors of Gynecology and Obstetrics, Massachusetts Medical Society, Phi Beta Kappa, Sigma Xi, Society for Gynecologic Investigation, and Society for Medical Decision Making
Disclosure: Nothing to disclose.
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