Myasthenia Ocular

Generality

Ocular myasthenia is a form of myasthenia gravis limited to the muscles of the eyes and eyelids.

Autoimmune disease, ocular myasthenia occurs because some autoantibodies inhibit the nervous mechanism that permits the contraction of the muscles belonging to the ocular compartment.

There are two typical symptoms of ocular myasthenia: diplopia (or double vision) and ptosis (or drooping eyelid).

Diagnosing ocular myasthenia is not always easy. For this reason, doctors must use different diagnostic tests.

Currently, there is no specific cure, but only a series of symptomatic treatments.

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Brief review of myasthenia gravis

Myasthenia gravis is a chronic autoimmune disease characterized by fatigue and weakness of some muscles.

At the base of myasthenia gravis there is an inefficient transmission of contractile nerve signals, which serve to activate the muscles of the human body.

Myasthenia gravis can involve muscles from multiple districts of the human body, from the eyes to the chest.

From the pathophysiological point of view, some autoantibodies cause myasthenia gravis, which, "turning" against the body to which they should provide protection, block the post-synaptic receptors of the neuromuscular junction and inhibit the excitatory effects of acetylcholine. By reducing the excitatory effects of acetylcholine, the affected patient experiences muscle weakness, especially when he has to use some muscles repeatedly.

Simplifying what has just been stated, at the origin of myasthenia gravis there is an anomalous behavior of some elements of the immune system; abnormal behavior that consists in going to hinder the transmission of nerve signals necessary for muscle contraction.

Currently, the treatment of myasthenia gravis consists of an immunosuppressive therapy, that is a therapy for the attenuation of the immune response.

What is ocular myasthenia?

Ocular myasthenia, or ocular myasthenia gravis, is a form of myasthenia gravis limited to the muscles of the eyes and eyelids .

It is, therefore, a chronic autoimmune disease, which - due to an abnormal behavior of some autoantibodies - determines an inappropriate transmission of the nerve signals necessary for the contraction of the muscles of the ocular compartment.

IT IS A MANIFESTATION OF MIASTENIA GRAVIS

Ocular myasthenia may appear individually or may be a manifestation of myasthenia gravis.

According to some statistical surveys, 90% of patients with myasthenia gravis have problems with eye and eyelid muscles, thus suffering from ocular myasthenia.

Epidemiology

Ocular myasthenia affects men and women equally.

It has a particular incidence in the population of Korean origin and in people suffering from thyroid diseases, thyme diseases or autoimmune diseases, such as scleroderma, erythematous systemic lupus, rheumatoid arthritis, Hashimoto's thyroiditis, multiple sclerosis and thyroid ophthalmopathy.

Causes

Being a form of myasthenia gravis, ocular myasthenia is an autoimmune disease .

Autoimmune diseases are particular morbid conditions, characterized by an exaggerated and improper response of the immune system . In fact, in individuals with an autoimmune disease, the cellular and glycoprotein elements that make up the immune system recognize some organs and / or tissues of the human body as foreign and, for this reason, they attack them.

The aggression that the immune system performs towards the body to be defended involves a more or less significant damage or alteration of the organs and tissues involved.

Currently, the precise reasons why the immune system turns against the organism to which it should protect are unknown.

Within this general framework, related to autoimmune diseases, ocular myasthenia is not an exception, so its triggering causes remain a mystery.

PATHOPHYSIOLOGY

As can be easily understood, the pathophysiology of ocular myasthenia is the same as that of myasthenia gravis. At the base of the condition in question, therefore, there is an anomalous behavior of some autoantibodies; anomalous behavior that leads to blockage of post-synaptic receptors of the neuromuscular junction and to the inhibition of the excitatory effects of acetylcholine.

Clearly, in the presence of ocular myasthenia the post-synaptic receptors involved are those that govern the contraction of the eye and eyelid muscles.

Symptoms, signs and complications

There are two characteristic symptoms of ocular myasthenia: double vision (or diplopia ) and palpebral ptosis (or drooping eyelid ).

The presence of diplopia depends on the involvement of a single extraocular muscle of one of the two eyes.

The palpebral ptosis, instead, derives from the impairment of the normal functioning of the levator muscle of the upper eyelid (ie the muscle responsible for the elevation of the eyelid). The drooping eyelid is a symptom that can be mono- or bilateral.

LESS COMMON SYMPTOMS

Among the less common symptoms of ocular myasthenia, the nystagmus and the so-called Cogan sign deserve a mention.

Nystagmus is the rapid and repeated movement of the eyeball due to muscle spasms.

Cogan's sign, on the other hand, consists of an abnormal upward movement of the upper eyelid, a movement that occurs after the gaze is kept down for 10-15 seconds.

FROM MYASTENIA GRAVIS TO EYE MIASTENIA

According to some statistical surveys, 75% of patients who develop myasthenia gravis manifest the first symptoms at the ocular and eyelid level.

Within two years, at least 80% of these patients develop symptoms in other anatomical districts of the human body (eg chest muscles).

If myasthenia gravis remains confined to the eyes and eyelids after 3 years, there is a 94% chance that the condition will not affect other muscles in other parts of the human body.

The lack of involvement of other muscles causes the ongoing pathological condition to take the specific name of ocular myasthenia.

Diagnosis

Ocular myasthenia can be quite difficult to diagnose, since, from a symptomatic point of view, it resembles different conditions and could be mistaken for one of these.

An error in the diagnostic phase can lead to failure to plan an adequate treatment or delay.

MOST COMMON DIAGNOSTIC ITER

In general, the diagnostic procedure to which the cases of suspicious myasthenia are subjected includes:

Physical examination and medical history;
Blood tests;
Electromyography;
The proof of the hydrophony;
Diagnostic imaging tests (eg: chest radiography). They are used by the doctor to rule out pathologies with symptoms similar to ocular myasthenia.

Therapy

Currently, there is no specific treatment for myasthenia gravis, but only a series of treatments to alleviate the symptoms ( symptomatic treatments ).

The list of symptomatic treatments of ocular myasthenia includes:

Administration of cholinesterase inhibitors (or anticholinesterase agents ). They are drugs that block cholinesterase, which is the enzyme that degrades acetylcholine.
The most used cholinesterase inhibitor in the case of ocular myasthenia is pyridostigmine.
Administration of corticosteroids . The doctors prescribe them with the intent to reduce the immune response and make the autoantibodies less aggressive, which prevent the mechanism of muscular contraction.
A corticosteroid widely used in cases of ocular myasthenia is prednisone.
Administration of immunosuppressants . The purpose of their use is the same as for the administration of corticosteroids: to reduce the immune response, to make autoantibodies less aggressive.
Azatoprine, methotrexate and cyclosporine are widely used in case of ocular myasthenia.
Surgical removal of the thymus . In some patients, this treatment leads to an improvement in the symptomatic picture. It remains a mystery why it is effective only for someone, while for others it is not at all.
Use of eye and sight supports . For diplopia, it can serve blindfold the eye that causes double vision or apply a special contact lens to it. For palpebral ptosis, doctors may recommend crutch spectacles or scleral contact lenses in order to support the drooping eyelid.