Myasthenia gravis

Myasthenia gravis is a rare autoimmune disease. It causes weak muscles and tiredness. Stress and hot weather can make the symptoms worse. It also gets worse with activity. 
Myasthenia gravis is caused by your immune system attacking the nerves that tell your muscles to contract. It is treated in two main ways. First, a drug can be given to slow down your immune system using an immunosuppressant like steroids. Alternatively, a drug can be given to turn up the signal that tells your muscles to contract. The signal for contracting is a chemical your body makes called acetylcholine. We turn up this signal by blocking acetylcholine breakdown - these drugs are called acetylcholinesterase inhibitors.