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Written by Lim Kenn Fui, Pharmacist.

What is Myasthenia Gravis?

Myasthenia Gravis is pronounced as (my-us-THEE-nee-uh GRAY-vis) and is a type of neuromuscular disorder that causes weakness in the muscles of our body. It is categorised as an autoimmune disorder where our own immune systems will block the connection between our nerves and muscles. This leads to a failure to control our own muscles which will cause weakness of the affected muscles.

Signs and Symptoms

Myasthenia gravis (MG) causes muscle weakness the more the muscle is and symptoms gradually improve once the muscle is in resting state. However, symptoms tend to worsen as the condition progresses after a few years of the onset of disease.

Below are the most common symptoms although the severity will vary according to individual:

  • Fatigue
  • Double vision
  • Difficulty breathing due to muscle weakness
  • Difficulty swallowing or chewing
  • Problems walking upstairs or lifting objects
  • Hoarse voice
  • Drooping of eyelids
  • Facial paralysis

The following factors may trigger or worsen exacerbations:

  • Menstruation
  • Worsening of chronic medical illnesses (cardiac, renal, autoimmune, etc.)
  • Immunization
  • Tapering of immunosuppression
  • Warm weather
  • Viral infections
  • Emotional stress
  • Pregnancy and postpartum period
  • Surgery
  • Medication

Causes

MG is an autoimmune disorder where our own antibodies will block the neuromuscular transmission to our skeletal muscles. Movement of our muscles depend chemicals called neurotransmitters(acetylcholine) to bind to receptors on the muscles. MG occurs when our own antibodies block or destroys the acetylcholine receptors for muscle movement and effectively leaving less receptors available for neurotransmitters to bind with. Without sufficient receptors our nerves are unable to send signals effectively to our muscles and eventually results to muscle weakness.

Another possible cause for MG is due to an organ called Thymus gland. Thymus gland is an organ situated on the upper part of our chest and is important in producing antibodies as part of our immune system. However, enlargement of the thymus gland or tumors can trigger or maintain the production of antibodies that blocks or destroy acetylcholine neurotransmitters.

According to the National Institutes of Health, MG typically occurs in people over the age of 40. Women are more likely to be diagnosed as younger adults, whereas men are more likely to be diagnosed at 60 or older.

Diagnosis

To diagnose MG a doctor will perform a complete physical exam, as well as take a detailed history of your symptoms. They’ll also do a neurological exam. This may consist of:

  • Check for muscle weakness
  • Reflex tests
  • Testing motor functions
  • Eye test and movements
  • Checking muscle tone

Other tests that can help your doctor diagnose the condition include:

  • Multiple nerve stimulation test
  • Blood test for presence of antibodies associated with MG
  • Edrophonium test is administered intravenously, and you’re asked to perform muscle movements under doctor observation
  • Imaging of the chest using CT scans  or MRI to rule out a tumor of Thymus gland
  • Electromyography

Treatment

As of now there is no cure for MG. The main form of treatment is mainly symptomatic control and also to suppress the immune system. The main type of medications will be corticosteroids or other type of immunosuppressant medication which helps to minimize the immune response to acetylcholine.

The Randomized Trial of Thymectomy in Myasthenia Gravis, a landmark study, has shown that trans-sternal thymectomy improves MG and even induces remission, or lessens the requirements or perhaps removes the need for prednisone and other immunosuppressants over a period of 3 years.

Complications

One of the most dangerous potential complications of MG is myasthenic crisis. Myasthenic crisis is a life-threatening condition that occurs when the muscles that control breathing become too weak to do their jobs. This consists of life-threatening muscle weakness that can include breathing problems. If you start to have trouble breathing or swallowing, contact your doctor or go to your local emergency room immediately.

References:

Davis, C. (2018). 12 Myasthenia Gravis Symptoms, Causes, Treatments & Cure. [online] MedicineNet. Available at: https://www.medicinenet.com/myasthenia_gravis/article.htm [Accessed 3 Jan. 2020].

Herndon, J. (2018). Myasthenia Gravis: Causes, Symptoms, and Diagnosis. [online] Healthline. Available at: https://www.healthline.com/health/myasthenia-gravis#causes [Accessed 3 Jan. 2020].

Jowkar, A. (2018). Myasthenia Gravis: Practice Essentials, Background, Anatomy. [online] Emedicine.medscape.com. Available at: https://emedicine.medscape.com/article/1171206-overview [Accessed 3 Jan. 2020].

Mayo Clinic. (n.d.). Myasthenia gravis – Symptoms and causes. [online] Available at: https://www.mayoclinic.org/diseases-conditions/myasthenia-gravis/symptoms-causes/syc-20352036 [Accessed 3 Jan. 2020].

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