Myasthenia gravis

Introduction
Myasthenia gravis is a type of autoimmune disorder which affects the neuromuscular junction. The patient suffers from weakness of the skeletal muscle that worsens towards the end of the day and with repeated efforts. The eye muscles are the first to be affected.

Myasthenia gravis can occur at any age. Females are more commonly affected and at an earlier age. Females are affected at the age of 10-40 years and males from 50-70 years. Prevalence is 3 cases per 100, 000 in the U.S. Familial cases are few.

What are the causes of Myasthenia gravis?
Circulating antibodies to the nicotinic acetylcholine receptors on muscles and a reduction in the number of receptors are the defects responsible for the findings in myasthenia gravis. The thymus is always abnormal, with 70% of the cases showing hyperplasia and 15% harboring a thymoma (tumor of thymus). It may also occur in patients receiving D-pencillamine.

What are the types of myasthenia?
To facilitate the treatment and staging the disease, the following classification is used:

I. Ocular myasthenia (15-20%)
II. A. Mild generalized myasthenia with slow progression; drug responsive (30%). B. Moderately severe generalized myasthenia; severe skeletal and bulbar involvement but no crises; drug response less than satisfactory (25%)
III. Acute fulminating myasthenia; rapid progression of severe symptoms with respiratory crises and poor drug response; high mortality (15%)
IV. Late severe myasthenia; symptoms as above, but resulting from steady progression over 2 years from class I to class II

What are the symptoms of Myasthenia gravis?
complain of inability to fix their hair because of the fatigue of their shoulders. There is more weakness towards the end of the day.

Fluctuating weakness is present. The weakness may vary over minutes or days. Prolonged changes are called remissions and exacerbations. Involvement of the respiratory muscles produces difficulty in breathing. It occurs in 10% of the myasthenia patients. There is increasing weakness during menstruation, exposure to very hot and cold climates and after vaccination.

Sometimes tingling and numbness of the face, hand and thighs occur, but it's very mild.

As the name implies, Myasthenia gravis is a muscular weakness with bad prognosis. Repeated or persistent activity of muscle group exhausts its contractile power, leading to weakness of the muscle. Rest restores the strength of the muscle to some extent. The onset of weakness is insidious, but in some patients it is fairly rapid. Some cases are initiated by emotional upset or respiratory tract infection. Once the disease begins, slow progression follows.

Usually muscles of the eyes are affected initially. It produces drooping of the eyelid (ptosis) and patient complaints of double vision (diplopia).Eye muscles are involved in more than 90% of the cases of myasthenia gravis. When the patient looks upwards for a prolonged period of time, the ptosis is exaggerated.

Muscles of mastication (chewing), facial expression (laughing, crying, blowing etc.,) and swallowing and speech are affected. Brain stem involvement produces difficulty in speaking and swallowing. The natural smile may become transformed into a snarl. Chewing food will be difficult and the patient may have to terminate a meal. Women may

What are the tests to find out myasthenia gravis?

• Positive response (improvement in the muscle power) to the test with cholinergic drugs like Neostigmine is confirmatory of myasthenia gravis.
• Tensilon test (using edrophonium) is the most often done test. The drug is short and quick acting.
• Electrodiagnostic studies- show decremental muscle action potential during repetitive nerve stimulation
• Positive assay for circulating Acetylcholine receptor antibodies is a sensitive and highly specific test.
• CT scan of the chest will show abnormality of the thymus if present.

Treatment of myasthenia gravis

• Anticholinesterase: It increases the acetylcholine at the receptors. Therapy should begin as soon as the diagnosis is made. Pyridostigmine, neostigmine and ambenonium are used.
• Thymectomy: appropriate for patients with thymoma (tumour of the thymus gland).
• Plamapheresis.
• Immunosuppression with corticosteroids and cyclophosphamide.
• Myasthenic crisis is a temporary exacerbation of myasthenia, which causes difficulty in breathing and weakness of all the limbs of the myasthenic patient. It is treated with intubation and artificial ventilation.

Did you know?
Myasthenia gravis can occur at any age. Females are more commonly affected and at an earlier age. Females are affected at the age of 10-40 years and males from 50-70 years. Prevalence is 3 cases per100, 000 in the U.S. Familial cases are few.