what is myasthenia gravis?

Answer 1

Myasthenia, is weakness of the muscles; myasthenia gravis, a chronic disease marked by abnormal fatigability and weakness of selected muscles, initially those around the eyes, mouth, and throat, resulting in drooping of the upper eyelid (ptosis), double vision, and dysarthria. It is an autoimmune disease in which the ability of the neurotransmitter acetylcholine to induce muscular contraction is impaired. Drug treatment and surgical removal of the thymus lessen the severity of the symptoms. Steroid therapy or plasma exchange may be used to treat the more severely affected patients.

Answer 2

it is a neuro muscular disorder caused by the failure of the muscles to recieve messages transmitted by the nerves causing paralysis. though they do not waste away or atrophy. it shows in the face first. there is no known cure

Answer 3

It is one form of muscular distrophy. The muscles lose it's sense of contraction, thus it's function.

Answer 4

A Neurological condition that affects muscles. check more out http://www.myasthenia.org/

Answer 5

its a muscle disorder

Answer 6

Background: Myasthenia gravis (MG) is a relatively rare autoimmune disorder of peripheral nerves in which antibodies form against acetylcholine (ACh) nicotinic postsynaptic receptors at the myoneural junction. A reduction in the number of ACh receptors results in a characteristic pattern of progressively reduced muscle strength with repeated use of the muscle and recovery of muscle strength following a period of rest.

The bulbar muscles are affected most commonly and most severely, but most patients also develop some degree of intermittent generalized weakness. The most important aspect of MG for emergency physicians is the detection and management of the myasthenic crisis, which is described below.

Pathophysiology: Autoantibodies develop against ACh nicotinic postsynaptic receptors for unknown reasons, although certain genotypes are more susceptible.

Cholinergic nerve conduction to striated muscle is impaired by a mechanical blockage of the binding site by antibodies and, ultimately, by destruction of the postsynaptic receptor.

Patients become symptomatic once the number of ACh receptors is reduced to approximately 30% of normal. The cholinergic receptors of smooth and cardiac muscle have a different antigenicity than skeletal muscle and are not affected by the disease.

The role of the thymus in the pathogenesis of MG is not entirely clear, but 75% of patients with MG have some degree of thymus abnormality (eg, hyperplasia in 85% of cases, thymoma in 15% of cases). Given the immunologic function of the thymus and the improvement in the clinical condition of patients following thymectomy, the thymus is suspected to be the site of autoantibody formation. However, the stimulus that initiates the autoimmune process has not been identified.

Frequency:

* In the US: The prevalence of MG in the United States ranges from 0.5-14.2 cases per 100,000 people. The prevalence has increased over the past 2 decades, primarily because of the increased life span of patients with the disease but also because of earlier diagnosis.

Mortality/Morbidity:

* In the past, untreated MG carried a mortality rate of 30-70%. In the modern era, patients with MG have a near-normal life expectancy.

* Morbidity results from intermittent impairment of muscle strength, which may cause aspiration, increased incidence of pneumonia, and falls. In addition, the medications used to control the disease may produce adverse effects.

Race: Onset of MG at a young age is slightly more common in Asians than in other races.

Sex:

* The male-to-female ratio in children and adults is 2:3.

* A female predominance exists in the young adult peak (ie, patients aged 20-30 y), and a slight male predominance exists in the older adult peak (ie, patients older than 50 y).

* The male-to-female ratio in children with MG and another autoimmune condition is 1:5.

Age: Onset peaks in neonates because of transfer of maternal autoantibodies, in those aged 20-30 years, and in those older than 50 years.
Physical: Patients with MG can present with a wide range of signs and symptoms, depending on the severity of the disease.

* Mild presentations of MG may be associated with only subtle findings, such as ptosis, that are limited to bulbar muscles. Findings may not be apparent unless muscle weakness is provoked by repetitive or sustained use of the muscles involved.

* Recovery of strength is seen after a period of rest or with application of ice to the affected muscle. Conversely, increased ambient or core temperature may worsen muscle weakness.

* Severe exacerbations of MG may present dramatically:

o Facial muscles may be slack, and face may be expressionless.

o Patient may be unable to support the head, which will fall onto the chest while the patient is seated.

o Jaw is slack.

o Voice has a nasal quality.

o Body is limp.

o Gag reflex is often absent, and such patients are at risk for aspiration of oral secretions.

* Respiratory distress

o The patient's ability to generate adequate ventilation and to clear bronchial secretions are of utmost concern with severe exacerbations of MG.

o Inability to cough leads to an accumulation of secretions; therefore, rales, rhonchi, and wheezes may be auscultated locally or diffusely. The patient may have evidence of pneumonia (ie, fever, cough, dyspnea, consolidation).

* Cholinergic crisis

o One of the confusing factors in treating patients with MG is that insufficient medication (ie, myasthenic crisis) and excessive medication (ie, cholinergic crisis) can present in similar ways.

o Cholinergic crisis results from an excess of cholinesterase inhibitors (ie, neostigmine, pyridostigmine, physostigmine) and resembles organophosphate poisoning. In this case, excessive ACh stimulation of striated muscle at nicotinic junctions produces flaccid muscle paralysis that is clinically indistinguishable from weakness due to MG.

o Myasthenic or cholinergic crisis may cause bronchospasm with wheezing, bronchorrhea, respiratory failure, diaphoresis, and cyanosis.

o Miosis and the SLUDGE syndrome (ie, salivation, lacrimation, urinary incontinence, diarrhea, GI upset and hypermotility, emesis) also may mark cholinergic crisis. However, these findings are not inevitably present.

Causes:

* The cause of MG is unknown, but it is clearly an autoimmune disease in which the specific antibody completely has been characterized.

* Females and people with certain human leukocyte antigen (HLA) types have a genetic predisposition to autoimmune diseases.

* As with other autoimmune diseases, a derangement of immune regulation occurs.

* Sensitization to a foreign antigen that has cross-reactivity with the nicotinic ACh receptor has been proposed as a case of MG, but the triggering antigen has not yet been identified.