Myasthenia gravis is an autoimmune disease whereby the nerve stimuli to voluntary muscles are blocked by antibodies. It can occur at any age and can be rapid or slow in its development.

It affects more females in children and younger age groups and more males in the older age groups and the overall incidence is about 17/100,000 people - so it is not a common disease for a GP with a list size of about 3,000 patients - yet, though not actually curable, it is a treatable condition and it can be dangerous to miss. There are various types of myasthenia.

Common Presenting Symptoms 

Eyes

There may be double vision, through weaker movements or a drooping eyelid, again caused through local muscle weakness.

Oral and Respiration

Difficulty in swallowing, and sometimes difficulty in speech. That can herald an emergency admission as it can lead to choking and can even lead to a myasthenic crisis. The voice may be weaker.

Limb Weakness

The weakness tends to affect the proximal muscles of the limbs, so that lifting one's arms or legs can show a weakness, patients often have difficulty getting out of the bath, or difficulty with steps and getting up from a chair due to thigh weakness.

The symptoms may be less obvious early in the day and may be worse at the end of the day or after exercise. Symptoms may also worsen in very hot situations - after a hot shower, or, having been lying down in the sun.

A characteristic sign in the limbs is that limb muscles fatigue very quickly, especially when doing repetitive exercises - repeated raising of a leg when lying down on a couch, or sideways raising of the arms - and similarly resisted movements of the arms or legs can show abnormal weakness.

Diagnosis

The first help in diagnosis is actually to consider the disease as a possibility. Some of the presenting symptoms in older people are slow in developing and can be very similar to other commoner old age causes.

A drooping eyelid is a common presentation and should alert one to follow-up possible causes. Similarly, variable double vision should bring the disease to mind, as should increasing weakness against resisted limb movements on examination. A variant of the disease is an ocular form that remains restricted to the drooping eyelid and / or double vision, although the ocular form can later develop into general myasthenia gravis.

Applying an ice-cold pad over a drooping eyelid that is caused by myasthenia, can show a short-term relief of the droop.

The presence of acetylcholine receptor antibodies in the blood is diagnostic, but not all cases may show that.

An Electromyography (EMG) test, usually requested by the neurologist, shows a characteristic falling of muscle activity, when subjected to repeated stimulation.

Treatment

Because of its rareness and some of the initial hazards in the illness, it is wise to refer the suspect patient to a neurologist, and people with myasthenia are often admitted to hospital to have the condition brought under stable condition.

The major hazard to avoid is a myasthenic crisis, in which the subject has a sudden acute difficulty in breathing. This can come on extremely quickly in patients whose illness is not under control and may require intubation - hence the advice to refer to a specialist on reasonable suspicion, so that a definite diagnosis can be established and corrective treatment commenced before the disease develops further.

Medication

This is usually commenced in hospital under supervision. Pyridostigmine (Mestinon®) tablets provide short-term symptom relief, but they do need to be taken very frequently. The aim of long-term treatment is to suppress the body's production of acetylcholine antibodies. It is not wise to increase the steroid dosage suddenly, as, in the short-term, this can worsen the symptoms.

Most patients require a steroids to induce and maintain remission. In severe cases, IVIG or plasma exchange may be used to gain rapid improvement (but such benefits only last eight weeks) and the patient is started on an incremental dose of steroids at the same time. In some patients, second-line immunosuppressant drugs, such as azathioprine, is added to try to reduce the steroid requirement, and thus, reduce long-terms steroid side-effects.

Cautions

Some common medications, including antibiotics, used for other concurrent illnesses, can exacerbate myasthenia. It is wise to check for drugs cautioned or contraindicated in patients with myasthenia.

Vaccinations

Being immunosuppressed makes it unwise for the subject to receive live vaccines.

Living with myasthenia

Once under control, people with myasthenia can live a reasonably normal life and have a normal life expectancy. The disease does affect people differently, but the general advice is to avoid getting tired and not to fill one's day too full with too many different things. Full days may be followed a day or two later with fatigue. It is also wise to be strict with one's medication regime, even when the disease has been well-controlled for a long time. It is helpful, if at all possible, to be treated for the condition by just one doctor.

Dr Jeremy Brewer

Advice from Fellow Practitioners