By-Mr ASHOK BISHNOI

Lecturer, JINR

Name is Latin and Greek in origin, literally means "grave muscle weakness“

Hallmark is variable and fatigable weakness of the skeletal (voluntary) muscles

Introduction:-

Normally impulses travel along the nerve to the ending and release the neurotransmitter substanceacetylcholine.

Acetylcholine travels through the neuromuscular junction and binds to acetylcholine receptors, which are activated, and generate a muscle contraction

In myasthenia gravis, person’s own antibodiesblock, alter, or destroy the receptors for acetylcholine at the neuromuscular junction, preventing muscle contraction

Thymus believed to be the site of antibody production

80% of MG people have thymus hyperplasiaor thymus tumor

80 – 90% of MG people have auto-antibodiesdirected at acetylcholine receptor sites

Why...?

“It is a chronic autoimmune disorder affecting the neuromuscular transmission of impulse in the voluntary muscle of the body” (skeletal muscle)

Definition:-

Women tend to get it earlier (20 – 40)

Men get it later (70 – 80)

Incidence;-

The exact cause of myasthenia gravis is not known

Risk Factor;-

Autoimmune attack

Thyroid gland abnormality

Etiology :-

Due to etiological factors

Lymphocyte produce acetylcholine receptor antibodies that attack the post synaptic muscle

membrane

Depletion of acetylcholine receptor of the neuromuscular junction

Defect in the transmission of impulse from nerve to muscle cell

Myasthenia gravis

Pathophysiology:-

Cardinal symptoms-

Fatigue

Weakness of eye muscle

Diplopia (double vision)

Ptosis (drooping of one or both eyelids)

Clinical Manifestation;-

Blood tests

Clinical and neurological examination

Imaging tests (e.g., x-ray, CT scan) (to detect enlarged thymus (thymoma), which is common in MG)

Intravenous anticholinesterase or Tensilon test

Neurological tests (e.g., electromyography) (evaluate muscle function

Blood tests are performed to determine serum levels of certain antibodies (e.g., AChR-binding antibodies, AChR-modulating antibodies, antistriationalantibodies). High levels of these antibodies may indicate MG.

Neurological examination involves testing muscles and reflexes. MG may cause abnormal eye movements, inability to move the eyes normally, and drooping eyelids. To test arm and leg muscles, the patient may be instructed to maintain a position against resistance for a period of time. Weakness that occurs during this test is called fatigability.

Chest x-ray and computed tomography (CT scan) may be performed to detect enlarged thymus (thymoma), which is common in MG.

The Tensilon test is often used to diagnose MG. The enzyme acetylcholinesterasebreaks down acetylcholine (ACh) after the muscle is stimulated, preventing prolonged muscle response to a single nerve impulse. Edrophonium chloride (Tensilon) is a drug that temporarily blocks the action of acetylcholinesterase.

In MG, there are few acetylcholine receptor sites (AChR) on the muscle and acetylcholine is broken down before it can fully stimulate the muscle, resulting in muscle weakness. By blocking the action of acetylcholinesterase, Tensilonprolongs muscle stimulation and temporarily improves strength.

In this test, Tensilon is administered intravenously (into a vein) and muscle response is evaluated. In cases of MG, muscle weakness improves within 1 minute. The Tensilon test is most effective when easily observed weakness is present, and is less useful for vague or fluctuating complaints. Side effects of the test include temporary abnormal heart rhythms such as rapid heart rate (atrial fibrillation) and slow heart rate (bradycardia).

Electromyography (EMG) uses electrodes to stimulate muscles and evaluate muscle function. Muscle contractions that become progressively weaker may indicate MG