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Myasthenia gravis

Definition:

Myasthenia Gravis (MG) is a chronic autoimmune neuromuscular disorder characterised by varying degrees of weakness of the voluntary muscles of the body. The hallmark of the disease is muscle weakness that increases during periods of activity and improves after periods of rest.

Epidemiology:

  • MG can affect individuals of any age, but there’s a notable peak among women in their 20s and 30s and men in their 50s and 60s.
  • The incidence is roughly 1.7-2.3 cases per 100,000 people per year, with a prevalence of about 15-20 cases per 100,000.

Aetiology:

  • The primary cause is an autoimmune response against the acetylcholine receptor (AChR) at the neuromuscular junction, leading to impaired transmission of impulses between nerve and muscle.
  • In some cases, MG is associated with thymomas or thymic hyperplasia.

Pathophysiology:

  • Autoantibodies (mainly IgG) are produced against the AChR or Muscle-Specific Kinase (MuSK), disrupting the normal neuromuscular transmission.
  • This results in voluntary muscle weakness, which is the primary symptom of MG.

Clinical Features

Signs and Symptoms:

  • Muscle weakness that worsens with activity and improves with rest.
  • Ocular muscle weakness leading to ptosis (drooping of one or both eyelids) and diplopia (double vision).
  • Bulbar muscle involvement can cause difficulties in swallowing, speaking, and chewing.
  • Generalised muscle weakness can affect limbs, neck, and respiratory muscles.

Diagnosis:

  • Clinical examination and history are crucial.
  • Acetylcholine receptor antibody test confirms the diagnosis in most cases.
  • Electromyography (EMG) shows a decremental muscle response to repetitive nerve stimulation.
  • Imaging studies, like CT or MRI of the chest, may be used to check for thymoma.

Management

Medications:

  • Anticholinesterase inhibitors (e.g., pyridostigmine) are often used to improve neuromuscular transmission.
  • Immunosuppressants (e.g., prednisone, azathioprine, mycophenolate mofetil) are used to suppress the abnormal immune response.
  • IV immunoglobulin (IVIg) and plasma exchange can be used for short-term symptom improvement in severe cases or as pre-operative preparation.

Surgical Treatment:

  • Thymectomy (removal of the thymus gland) is recommended for patients with thymoma and may improve symptoms in non-thymomatous MG patients.

Supportive Therapy:

  • Physical therapy and occupational therapy may help to maintain muscle function and cope with muscle weakness.

Prognosis

  • With treatment, most individuals with MG can lead normal or nearly normal lives.
  • The severity of the disease varies widely among individuals; some may experience only ocular symptoms, while others may have widespread muscle weakness.
  • Early diagnosis and treatment are key to managing symptoms effectively.

Summary

Myasthenia Gravis is a complex autoimmune disorder requiring a multidisciplinary approach for management. Understanding its pathophysiology, clinical presentation, and treatment options is essential for providing comprehensive care to patients. Early intervention and individualised treatment plans can significantly improve the quality of life for those affected.

One Comment

  1. Hannah Marshall says:

    hia – this page is glitched and is about migraines not MG

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