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Myasthenia gravis

Myasthenia gravis


Introduction-
an autoimmune disorder of neuromuscular            junction. It is caused due to production of antibodies against the Nm receptors of NMJ that results in a decrease in the number of Nm receptors.

It is characterized by grave weakness of the          muscle due to the inability of neuromuscular       junction to transmit impulses from nerve to           the  muscle. It is a serious and sometimes a fatal disease.

Causes of myasthenia gravis


 The main cause is Development of antibodies (IgG) against the receptors of Ach (acetylcholine).
 Body develops antibodies against its own Ach receptors. IgG antibodies destroy the receptors.

Symptoms of myasthenia gravis


  Common symptoms

  Slow and weak muscular contraction because of the defective neuromuscular activity. Inability to maintain the prolonged contraction of the skeletal muscle. Difficulty in speech due to weakness of muscles of speech.(dysphonia)

  Difficulty in swallowing due to weakness of throat muscles.(dysphagia). Quick fatigability when the patient attempts repeated muscular contraction. Weakness and fatigability of arms and legs.

Double vision (diplopia) and droopy eyelids  (ptosis) due to the weakness of ocular muscle.

in severe conditions-
 paralysis of muscles occurs and patient dies mostly due to paralysis of respiratory muscles.

*Muscles which are more susceptible for myasthenia gravis-
 - Muscles of neck
 - Muscles of limbs
 - Muscles of eyeball
 - Muscles responsible for movement of eyelids
 - Muscles responsible for chewing
 - Muscles responsible for swallowing
 - Muscles responsible for speech
 - Muscles responsible for respiration

Diagnosis of myasthenia gravis

 Edrophonium test-
 Edrophonium(2-10mg) given slow i.v. shows dramatic improvement of symptoms in patients with myasthenia gravis but not in muscular dystrophy.

Treatment of myasthenia gravis


 treatment of myasthenia gravis is  administration of inhibitors of cholinesterase
(Anticholinesterase), Neostigmine and Pyridostigmine.

Additional knowledge

There is an increased incidence of  myasthenia gravis in patients with thymoma.
Thymoma is a tumor originating from the epithelial cells of the thymus gland.

Myasthenia gravis is a example of type 2 hypersensitivity reactions.
  

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