Myasthenia gravis explained

What myasthenia gravis is

Muscles move when nerves send them a chemical message across a tiny gap called the neuromuscular junction. In myasthenia gravis, the immune system mistakenly makes antibodies that block or damage the receptors that receive this message. As a result, fewer signals get through, and the muscle grows weak — particularly when it is used repeatedly. A key feature is that weakness gets worse with activity and improves with rest, so muscles are often stronger in the morning and weaker by evening. It is an autoimmune condition, meaning the body's defences turn on its own tissues. The thymus gland in the chest is often involved and may be enlarged or contain a growth called a thymoma, which is why the thymus is checked as part of assessment.

Common symptoms

The most common first signs involve the eyes: a drooping eyelid on one or both sides, and double vision as the eye muscles tire. In many people, weakness spreads to other muscles. Facial and throat muscles can be affected, leading to a change in the smile, difficulty chewing, slurred or nasal speech, and trouble swallowing. The neck and limb muscles may tire, making the arms heavy when lifting or the legs weak on stairs. A hallmark is that symptoms fluctuate — better after rest, worse with effort, heat, stress or infection. In some people only the eyes are affected, called ocular myasthenia; in others the weakness is more widespread, called generalised myasthenia. The most serious concern is weakness of the breathing muscles, which is uncommon but dangerous.

How it is diagnosed

Diagnosis usually starts with a careful history and examination looking for fatigable weakness — muscles that weaken as they are tested repeatedly. Blood tests can detect the antibodies involved, most commonly antibodies against the acetylcholine receptor, and other antibodies such as anti-MuSK in some people. Nerve and muscle tests, including repetitive nerve stimulation and single-fibre studies, measure how well the nerve-to-muscle signal holds up. A CT or MRI scan of the chest checks the thymus gland for enlargement or a thymoma. Because symptoms can mimic other conditions, diagnosis is made by a neurologist piecing together the pattern of weakness, the antibody results and the nerve tests. Getting the right diagnosis matters, as treatment is specific and effective.

Treatment and living well

Treatment aims to improve the nerve-to-muscle signal and to calm the overactive immune system. Medicines that boost the chemical messenger can quickly improve strength, while medicines that dampen the immune system — including steroids and other immune-modifying drugs — reduce the underlying attack over time. For selected people, removing the thymus gland can improve symptoms or reduce the medicines needed, especially if a thymoma is present. During flares, hospital treatments that filter or replace antibodies can help. Alongside medicines, pacing activity, resting when tired, managing heat and stress, and treating infections promptly all help. Certain medicines can worsen myasthenia, so it is important that any new prescription is checked against the condition. With specialist care, most people find their symptoms become well controlled.

Myasthenic crisis: a warning

The most serious complication is a myasthenic crisis, when weakness of the breathing and swallowing muscles becomes severe. This can be triggered by infection, stress, surgery, some medicines or missed treatment. Warning signs include increasing shortness of breath, difficulty swallowing or coughing, a weak voice, and severe or rapidly worsening weakness. A crisis is a medical emergency because breathing can fail, and some people need support with a ventilator in hospital until treatment takes effect. Anyone with myasthenia and their family should know these red flags and seek urgent help early rather than waiting. Because a crisis can build quickly, difficulty breathing or swallowing should never be ignored. Prompt hospital treatment is very effective, and people usually recover well once the crisis is managed.