Also found in: Dictionary, Thesaurus, Encyclopedia.
Related to myasthenic: Myasthenic crisis


Relating to myasthenia.
Farlex Partner Medical Dictionary © Farlex 2012


Relating to myasthenia.
Medical Dictionary for the Health Professions and Nursing © Farlex 2012


(mī″ăs-thē′nē-ă) [ my- + -asthenia]
Muscular weakness and abnormal fatigue. myasthenic (-then′ik), adjective

myasthenia gravis

Abbreviation: MG
An autoimmune motor disorder marked by muscular fatigue that develops with repetitive muscle use and improves with rest or with the application of a cold pack. It is caused by antibodies to the acetylcholine receptor in the neuromuscular junction and a decrease in receptor sites for acetylcholine. Because the smallest concentration of acetylcholine receptors in the body is in the cranial nerves, weakness and fatigue of the eye muscles, muscles of mastication, and pharyngeal muscles are the most prominently affected in most patients, but any (skeletal) muscle group may be involved. The disease is rare, affecting about 14 people out of 100,000.


Diagnosis is made on the basis of patient history, a thorough neurological examination, electromyography, repetitive nerve stimulation, a Tensilon test, or a combination of these tests. Intravenous injection of Tensilon significantly improves muscle weakness within 60 sec, lasting up to 30 min Acetylcholinesterase receptor antibody titers in the blood are elevated in about 50% to 70% of patients with myasthenia gravis.


Clinical signs include ptosis of the eyelid and double vision due to fatigue and weakness in the extraocular muscles, and difficulty chewing and swallowing from impaired facial and pharyngeal muscles. Speech that becomes progressively more dysarthric during prolonged dialogue is another common symptom. Symptoms are exacerbated by repetitive muscle use, and, in some patients, by menses, emotional stress, prolonged exposure to sunlight or cold, and infections. Myasthenia gravis crisis is a sudden exacerbation of symptoms with respiratory failure.


The primary treatment is with anticholinesterases and immunosuppressive agents. Anticholinesterase therapy often becomes less effective as the disease worsens. In selected patients, removal of the thymus, plasmapheresis, or immunoglobulin therapy is used.

Patient care

The patient with MG should seek medical attention immediately if he or she experiences difficulty breathing, talking, chewing, or swallowing. These symptoms may herald a myasthenic crisis. In crisis the patient's cardiovascular, neurologic, and respiratory status should be monitored in an intensive care unit. Suctioning the airway and postural changes may sometimes maintain adequate oxygenation and ventilation. If not, the patient will need intubation and positive-pressure ventilation. Exercise, meals, and care activities should be planned around medication-induced energy peaks. The patient should be taught that soft but solid foods are more easily managed than liquids when swallowing is difficult. Additional help for patients is available through support groups and Internet-based resources such as the Myasthenia Gravis Foundation of America (


Because edrophonium (Tensilon) occasionally causes significant bradycardia or asystole, atropine should be kept at the bedside of any patient given this medication.
Medical Dictionary, © 2009 Farlex and Partners
References in periodicals archive ?
Literature review of the usefulness of repetitive nerve stimulation and single fiber EMG in the electrodiagnostic evaluation of patients with suspected myasthenia gravis or Lambert-Eaton myasthenic syndrome.
Electrophysiological diagnostic criteria of lambert-Eaton myasthenic syndrome.
(5,16) Plasmapheresis is used as an option for patients in myasthenic crisis and before thymectomy (2,6,7) Its benefits can last up to six weeks, (5) but there can be complications and side effects.
To study the predisposing factors, clinical features, associated complications and treatment outcome in patients with myasthenic crisis.
Shelton, "Myasthenia gravis and congenital myasthenic syndromes in dogs and cats: A history and mini-review," Neuromuscular Disorders, vol.
Lambert-Eaton myasthenic syndrome: from clinical characteristics to therapeutic strategies.
Because of her spared pupils and normal accommodation reflex, bulbar sign, and progressive quadriparesis, we started treatment with the impression of myasthenic crisis.
Farvid, "Emotional stress as a trigger of myasthenic crisis and concomitant takotsubo cardiomyopathy: a case report," Journal of Medical Case Reports, article 393, 2010.
The seven-year-old female patient presented in this case report had failed initial treatment with anticholinesterase and had undergone monthly intravenous immunoglobulin (IVIG) for nearly one year when she developed myasthenic crisis necessitating mechanical ventilation.
Iron deficiency causes rapid depletion of iron-dependent oxidative enzymes which results in myasthenic changes in muscles of alimentary tract, causing mucosal degeneration, muscle atrophy, and esophageal web formation, and also leads to neoplastic changes of the pharynx and upper esophagus.
However, Tensilon test (TT) and electromyography (EMG) were both suggestive of generalized MG, excluding the congenital myasthenic syndromes and other conditions mimicking MG.
Lambert-Eaton myasthenic syndrome antibodies (voltage gate calcium channel (VGCC) antibodies) were also negative.