Myasthenia gravisMyasthenia gravis

Myasthenia Gravis

• It is an autoimmune disorder affecting the myoneural junction, is characterized by varying degrees of weakness of the voluntary muscles.

• A disorder of neuromuscular function thought to be due to the presence of antibodies to acetylcholine receptors at the neuromuscular junction (NMJ).

Incidence

• MG occurs in all ethnic groups and both genders.

• It most commonly affects young adult women (<40 years) & older men (>60 years), but it can occur at any age.

Prevalence

• Today there are an estimated 50,000 cases in the US.

• MG can be found in anyone, but it is “most common in females around the third decade of life.

Etiology

• The Unknown cause.

• Defect in the transmission of nerve impulses to muscles.

• Antibodies against acetyl choline receptors at the NMJ.

• Thymic abnormalities.

Pathophysiology

• Autoantibodies against acetylcholine receptor sites.

• Impaired transmission of impulses across the myoneural junction.

• Availability of fewer receptors for stimulation.

• Volunatary muscle weakness that escalates with continued activity.

Clinical Manifestations

• Ocular symptoms- Diplopia, ptosis.

• Bulbar symptoms- Weakness of the muscles of the face & throat, and generalized weakness, and expressionless face.

• Weakness of the jaw muscles allaws the mouth to open.

• Dysphonia.

• The generalised weakness of all the extremities and the intercostal muscles, resulting in decreasing vital capacity and respiratory failure.

• Weakness of neck muscles may result in lolling of the head.

• Laryngeal involvement produces dysphonia and increases the patients risk for choking, dysphagia and aspiration.

Diagnosis

• History

• Physical examination

• Anticholinesterase test

• Acetylcholine receptor antibody titers

Medical management

• Anticholinesterase drugs. (pyridostigmine bromide)

• Immunosuppressive therapy. (prednisolone)

• Plasmapharesis.

• Intravenous immunoglobulin (IVIG) therapy.

• Thymectomy.

Complications

Myasthenic crisis

A myasthenic crisis is an exacerbation of the myasthenia gravis process characterised by severe generalised muscle weakness and respiratory and bulbar weakness that may result in respiratory failure.

Treatment of myasthenic crisis

• Neostigmine methylsulfate -IM/IV

• Plasmapharesis and IVIG

• Endotracheal intubation and mechanical ventilation

Cholinergic crisis

Anticholinergic overmedication leads to cholinergic crisis. The symptoms are similar to myasthenic crisis.

• Treatment- Withdraw the anticholinergic medication and administer Atropine sulfate (antidote to anticholinesterase drugs)

• Endotracheal intubation and mechanical ventilation

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