Seronegative myasthenia gravis: when the antibody test is normal

Myasthenia gravis is an autoimmune condition. The NHS explains that the immune system mistakenly damages the communication system between the nerves and the muscles, making the muscles weak and easily tired. It is linked to the thymus gland, a small gland in the chest, which is larger than normal in many people with the condition. Around 1 in 10 people have an abnormal growth of the thymus called a thymoma.

The condition can affect people of any age, typically starting in women under 40 and men over 60. Common symptoms include droopy eyelids, double vision, difficulty making facial expressions, problems chewing and swallowing, slurred speech, weak arms, legs or neck, and shortness of breath. The NHS says symptoms tend to get worse when you are tired and are often worse towards the end of the day and better the next morning.

Seronegative means that the antibody blood test is negative, that is, it does not show the raised level that is typical of myasthenia gravis. The NHS describes the main blood test as looking for a type of antibody that stops signals being sent between nerves and muscles, and says that a high level usually means you have myasthenia gravis. It then makes a point that matters for anyone with a normal result: not everyone with the condition will have a high level of antibodies, particularly if it is only affecting the eye muscles.

The NHS pages read for this guide do not describe other antibody types or give figures for how many people are seronegative, so this page does not either. The practical message is that a normal antibody result does not rule the diagnosis out when the symptoms and other tests point towards it, and the neurology team may repeat the blood test later if symptoms continue or get worse.

The NHS says myasthenia gravis can be difficult to diagnose and several tests may be needed. A GP asks about your medical history and symptoms, and an optician may notice problems such as double vision or eyelid droop. If a problem with the brain or nerves is suspected, you may be referred to a specialist in hospital for tests to diagnose myasthenia gravis and rule out other conditions with similar symptoms.

Treatment aims to keep symptoms under control so that you can live a largely normal life. The NHS suggests avoiding triggers such as tiredness, stress, infections, certain medicines and surgery without telling the surgeon about your condition. Pyridostigmine is usually the first medicine and helps signals travel between nerves and muscles, but it only lasts a few hours so needs to be taken several times a day.

If that is not enough, steroid tablets such as prednisolone may be used to reduce immune activity, and immunosuppressants such as azathioprine or mycophenolate if steroids do not control symptoms, a high dose is needed or side effects are significant. The NHS says these take at least around 3 months and 6 months respectively to work and need regular blood tests. Thymectomy, surgery to remove the thymus, may be recommended and has been shown to improve symptoms in some people with an unusually large thymus. It is not always effective.

A myasthenic crisis, with severe breathing or swallowing problems, is a medical emergency needing urgent hospital treatment, which may include oxygen, a ventilator, intravenous immunoglobulin or plasmapheresis. If you drive, the NHS says you should tell the DVLA you have myasthenia gravis.

The NHS says myasthenia gravis is a long-term condition that typically has phases when it improves and phases when it gets worse, with flare-ups followed by periods of remission. It usually spreads from the eyes and face to other areas over weeks, months or years, though for some people only the eyes are affected. If severe it can be life threatening, but it does not have a significant impact on life expectancy for most people.

The NHS notes that your clinical team will pass information about you to the National Congenital Anomaly and Rare Disease Registration Service, which you can opt out of. It names Myaware as the main UK charity for people with myasthenia gravis and their families.

On the NHS the route runs through a GP to neurology, with specialist neuromuscular clinics for ongoing care. Private neurology can offer quicker access to repeat testing and nerve studies. If a first antibody test is normal and you are still symptomatic, ask whether the test will be repeated and which other tests are planned, and note when your symptoms are better or worse, as the NHS says they tend to be worse when you are tired and towards the end of the day.