Myasthenia gravis

Myasthenia gravis is an autoimmune disease, that is to say, our immune system, a defense system, mistakenly attacks healthy tissue.

In normal conditions, the muscles work because their receptors receive chemical substances (neurotransmitters) from the nerve endings. 

In the case of myasthenia gravis, the immune system creates antibodies that harm and destroy many of the acetylcholine receptors (neurotransmitters) that are found in a type of muscle, which we control voluntarily, in such a way that it breaks normal communication between the nerve and the muscle and it gets tired and weak and does not work properly. 

When it detects fewer chemical products, the muscle finds this contraction difficult thereby causing fluctuating muscle weakness and tiredness in different muscle groups.

In terms of ophthalmology, the most common symptom is droopy eyelids (ptosis) which gets worse throughout the day. It is usually bilateral and may be asymmetrical. The patient explains that they wake up feeling well and then start feeling worse to the point that at the end of the day they cannot even open their eyes. 

It is common that such worsening also happens when the patient is sick, physically or mentally exhausted or stressed. In addition, other eye symptoms may arise such as double vision, with the same behaviour as droopy eyelids and the same trigger factors.

Generally speaking and in less common cases, painless weakness, tired arms and legs as well as difficulty in making gestures, pronouncing, articulating (dysarthria), chewing, swallowing (dysphagia) and breathing may occur. 

There are no clear risk factors linked to myasthenia gravis. It may affect any individual, but it is more prevalent in young women from the age of 20 to 40 and men from the age of 60.

It is right to say that myasthenia gravis may, in some cases, be associated with patients suffering from a thymoma (a benign or malignant neoplasm that affects the thymus increasing its size and altering its functionality). It may also be associated with other autoimmune diseases.

Systemic myasthenia gravis

This myasthenia typically affects elderly people. It affects the whole body in the form of tiredness and fatigue often caused by physical exercise and accompanied by eye symptoms such as double vision and droopy eyelids on many occasions.

The fatigue affects the arms and legs but it may also impact the facial expression, speech, breathing and chewing. The signs that a doctor may observe are weakness of the distal muscles of the upper limbs and proximal muscles of the lower limbs, leading to atrophy in advanced cases. 

A myasthenic crisis is the height of the systemic symptoms, which may lead to death through an inability to breathe if it is not treated urgently. 

Ocular myasthenia

The eyes are affected in 90% of cases and it is the most common form of presentation, amounting to 60% of all myasthenias. It causes latent droopy eyelids, in both eyes but in an asymmetrical and irregular way. 

As mentioned above, these droopy eyelids worsen at the end of the day with the eyes turning upward. Another symptom associated with this type of myasthenia is double vision, most commonly vertical, although it may be any other type.

On occasions, it may also be accompanied by nystagmus of the eye, which is uncontrollable and involuntary movements of the eye that happen quickly and repetitively. These movements may be side to side (horizontal), up and down (vertical), circular (rotary) or a combination thereof.  

If you have symptoms, you should see your ophthalmologist. You will usually be referred to a neurologist to proceed with treatment.