Myasthenia Gravis

Myasthenia Gravis

Myasthenia Gravis is an autoimmune neuromuscular disorder. It causes rapid fatigue in voluntary muscles and progressive voluntary muscle weakness. The body develops antibodies that damage nicotinic receptors present in the muscle. This causes a breakdown in communication between nerves and muscles. The extent of nicotinic receptor damage and muscle weakness depends upon various factors like physical stress, emotional stress, menstruation, pregnancy, infection, etc.

Myasthenia Gravis Symptoms

• · Eye Muscle Weakness

• · Eyelids Drooping (Ptosis)

• · Blurred/ Double Vision (Diplopia)

• · Facial Expression Change

• · Swallowing Problem

• · Shortness of Breathing

• · Impaired Speech

• · Muscle Weakness: Legs, Arms, Fingers, Neck

Diagnosis: Muscle weakness develops due to various reasons. Thus before the start of treatment, it must be properly diagnosed. In myasthenia gravis, muscle weakness is mainly due to a reduction in nicotinic receptor (Acetylcholine receptor). Thus, acetylcholine cannot perform its physiological functions.

An overdose of acetylcholine also causes muscle weakness. It is called a cholinergic crisis.

To diagnose the reason for muscle weakness edrophonium 2 mg is administered followed by 8 mg at intervals of 45 minutes. Edrophonium is an effective acetylcholine esoteric site inhibitor. However, it is not a foolproof diagnostic procedure because several times edrophonium gives a false-positive result. Blood tests, nerve tests, and MRI scans are used to diagnose Myasthenia Gravis.

Treatment; Anticholinestearase drugs prolong the duration of action of acetylcholine at the neuromuscular junction. These drugs increase the biological effect of acetylcholine. Neostigmine salicylate is administered orally three times a day or four times a day. The dose is gradually increased till optimum effect is achieved.

Pyridostigmine or ambenonium are equally effective. In the initial stage of treatment, the muscarinic effect of these drugs also appears as a side effect. It can be controlled by using atropine sulfate. However, on chronic administration of these drugs, the body develops tolerance to the muscarinic effect of these drugs.

Ephedrine sulfate is also used as a supplement to the above anticholinesterase drugs. Corticosteroids have an immunosuppressant effect. They inhibit the formation of antibodies damaging nicotinic receptors. But their long-term uses precipitate serious side effects. Prednisolone is used in an advanced stage of myasthenia gravis.

Difference between Myasthenia Gravis and Cholinergic Crisis

Myasthenia gravis (MG) and cholinergic crisis are both conditions related to neuromuscular transmission. However, they have different underlying causes. The following are some differences between the two:

1. Underlying Cause:

   • Myasthenia Gravis (MG): It is an autoimmune disorder. The body's immune system targets and attacks acetylcholine receptors at the neuromuscular junction, This leads to muscle weakness and fatigue.

   • Cholinergic Crisis: This condition is caused by an overdose of cholinergic medications to treat MG. These medications, such as cholinesterase inhibitors (e.g., pyridostigmine), increase acetylcholine levels. It leads to excessive stimulation of nicotinic and muscarinic receptors.

2. Clinical Presentation:

   • Myasthenia Gravis (MG): Symptoms include muscle weakness and fatigue. It worsens with activity and improves with rest. Weakness starts in the eye muscles (ptosis or double vision) but can affect any voluntary muscle group.

   • Cholinergic Crisis: Symptoms include muscle weakness, respiratory distress, excessive salivation, sweating, and miosis (constricted pupils). The weakness in the cholinergic crisis is more severe than the usual fluctuating weakness seen in MG.

3. Triggering Factors:

   • Myasthenia Gravis (MG): Exacerbations of MG symptoms may be triggered by stress, infection, fatigue, or certain medications.

   • Cholinergic Crisis: It is triggered by an excessive dose of cholinesterase inhibitors used to manage MG.

4. Response to Tensilon (Edrophonium) Test:

   • Myasthenia Gravis (MG): Tensilon test, involving the administration of edrophonium. It temporarily improves muscle strength in MG patients.

   • Cholinergic Crisis: Tensilon test worsens symptoms in cholinergic crisis due to increased acetylcholine levels.

5. Treatment:

   • Myasthenia Gravis (MG): Treatment involves medications that enhance neuromuscular transmission (cholinesterase inhibitors), immunosuppressants, and, in some cases, thymectomy.

   • Cholinergic Crisis: Treatment involves discontinuing cholinesterase inhibitors, supportive care, and in severe cases, the administration of atropine (an antimuscarinic drug) to counteract excessive cholinergic stimulation.

It's important to note that distinguishing between myasthenia gravis and cholinergic crisis often requires a detailed clinical evaluation, including the patient's medical history, physical examination, and sometimes diagnostic tests. If someone is experiencing symptoms suggestive of these conditions, they should seek prompt medical attention for an accurate diagnosis and appropriate management