Ocular Myasthenia Gravis - A Walkthrough

Introduction:

Myasthenia gravis (MG), also called "snowflake disease", is a chronic autoimmune disorder in which the communication between the nerves and muscles is collapsed by the antibodies. This results in the weakness of the voluntary skeletal muscles, especially in controlling the eyes, mouth, throat, and limbs. Myasthenia gravis is neither inherited nor contagious. The cause of the disease is not known, but people of any age are susceptible to it. The diagnosis is crucial, but prompt medical management helps patients live longer.

What Is Ocular Myasthenia Gravis (OMG)?

Myasthenia gravis (MG), an autoimmune neuromuscular disease characterized by fatigue and muscle weakness, has a subtype known as ocular myasthenia gravis (OMG). The muscles that guide the movement of the eyes and eyelids are the only areas of weakness in OMG. In OMG, the immune system mistakenly targets the acetylcholine receptors (AChR) at the neuromuscular junction, which transfers nerve signals to muscles. These receptors are necessary for muscle contraction, and when the immune system attacks them, nerve-muscle transmission is broken. Approximately 85 % of patients who initially present with MG's ocular signs and symptoms will progress to systemic MG within two years.

What Are the Types of Myasthenia Gravis?

According to the National Organization for Rare Disorders (NORD), suggests three types of myasthenia gravis:

• Ocular - Affecting the eyes.

• Generalized - Impacting many muscles in the body.

• Transient neonatal - Occurring among some babies born to women with MG.

How About the Prevalence of Ocular Myasthenia Gravis?

Ocular myasthenia gravis is generally considered to be less common than generalized myasthenia gravis, although its frequency varies. Myasthenia gravis is estimated to affect 20 people out of every 100,000 people. Although OMG can affect people of any age, it typically affects younger people, primarily those in their 20s and 30s.

The ocular subtype of myasthenia gravis can be particularly challenging to diagnose due to its variable symptoms and tendency to overlap with other neurological disorders. A thorough medical evaluation with specialized testing is typically necessary to obtain an accurate diagnosis.

What Are the Manifestations of Ocular Myasthenia Gravis?

Ocular myasthenia gravis (OMG) is a disorder marked by weakness and exhaustion in the muscles responsible for moving the eyes and shutting the eyelids. The levator palpebrae superioris, extraocular muscles, orbicularis oculi, and facial expression muscles are the most frequently affected muscles. The following are the primary symptoms of OMG:

1. Ptosis:

• Ptosis is the drooping of the upper eyelids.

• One of the most prevalent signs and symptoms of MG is ptosis.

• Levator palpebrae superioris (LPS) involvement is the main cause of ptosis.

• It can be bilateral or unilateral, and when it is bilateral, it is frequently asymmetrical.

• Ptosis may worsen following an extended period of upgaze, sometimes known as the "lid fatigability test”.

• The Cogan's lid twitch is another clinical sign characterized by a brief upward overshoot that is followed by a downward drift of the upper lid after staring down for at least 15 seconds. Cogan's lid twitch, however, is not unique to MG of the eyes.

2. Diplopia:

• One of the primary indicators and symptoms of OMG is diplopia or double vision.

• This occurs when the eye muscles weaken, and the eyes are misaligned, resulting in the perception of two images of the same object.

• The effects of double vision may be apparent in certain directions.

3. Peek Sign:

• A peek sign appears due to orbicularis muscle fatigue.

• When the patient closes their eyelids for extended periods, the sclera will be visible due to the parting of the eyelids in the absence of forced opening.

How Is Ocular Myasthenia Gravis Diagnosed?

A multidisciplinary approach, frequently headed by a neurologist or neuromuscular specialist, may be necessary to diagnose ocular myasthenia gravis. The diagnosis involves a physical examination, specific tests, and blood tests.

• Physical Examination: The healthcare provider looks for the symptoms of double vision, drooping eyelids, and eye muscle weakness by examining the eye movements and eyelid function.

• Ice Pack Test: On applying the ice pack to the affected eye, drooping of the eyelids improves. This helps to confirm the diagnosis.

• Blood Tests: Blood tests are done to measure the anti-acetylcholine receptor antibodies or anti-muscle-specific kinase antibodies, which are usually found elevated in myasthenia gravis.

• Electromyography: Electrical activity in muscles is recorded.

• Imaging Studies: Because thymus abnormalities are indicative of myasthenia gravis, thymus assessments are performed using CT and MRI scans.

How Is Ocular Myasthenia Gravis Managed?

The treatment aims to achieve disease remission, minimize drug-induced side effects, improve muscle weakness (which reduces diplopia and ptosis symptoms), and slow or stop the progression of the condition to generalized MG. Management of the condition includes:

1. Acetylcholinesterase Inhibitors: These are the first-line drugs that, on administration, enhance the nerve impulse transmission to muscle, thus improving muscle strength.

2. Immunosuppressants: These drugs are given when the symptoms worsen and persist by acting on the neuromuscular junction.

3. Thymectomy: Surgical removal of the thymus gland is advised when the thymus is abnormal or if the patient is younger. The symptoms improve after thymectomy.

4. Immunoglobulin Therapy: Intravenous immunoglobulin can be administered to improve the immune system.

5. Plasma Exchange (Plasmapheresis): On removing blood plasma to replace it with donor plasma, temporary relief from the symptoms is obtained.

6. Botox Injections: Botulinum toxin (botox) injections temporarily improve the symptoms.

Is There a Way to Prevent Ocular Myasthenia Gravis?

The strategies to prevent ocular myasthenia gravis are:

• Avoid the potential triggers that worsen symptoms and disease progression.

• Maintaining a healthy lifestyle, like a balanced diet, regular exercise, and adequate sleep, contributes to overall well-being.

• Manage stress by doing yoga, meditation, and deep breathing exercises.

• Early detection prevents disease progression.

• Adhere to prescribed medications if diagnosed with myasthenia gravis.

Conclusion:

Though ocular myasthenia gravis is a focal form of MG, it needs multidisciplinary management. The disease strikes people of any age and gender, irrespective of race and ethnicity. Diagnosis is very important in myasthenia gravis to differentiate between the types to curate the treatment plan. Neuro-ophthalmology patient education is important to protect eye health. The healthcare provider must look for reliable biomarkers to prevent disease progression.