Myasthenia Gravis is an autoimmune disorder that is caused by antibodies that bind to postsynaptic acetylcholine (ACh) receptors located at the NMJ (Neuromuscular junction). It most commonly affects young adult women and older men, and the peak incidence in women is age 20 to 30; in men, 50 to 70. It is more common in women and can be associated with thymoma, thyrotoxicosis, and other autoimmune disorders.
Sign and Symptoms of Myasthenia gravis
- Presents with fluctuating muscle weakness, ptosis or double vision,
- Bulbar symptoms (eg, dysarthria, dysphagia), and proximal muscle weakness.
- Symptoms typically worsen with fatigue at the end of the day. Patients may report difficulty in swallowing, climbing stairs and rising from a chair.
- Bulbar weakness is prominent in MuSK antibody-positive MG.
- Limb weakness is often proximal & asymmetric
- Tendon reflexes are unaffected
- Myasthenic crisis is rare but can cause life-threatening conditions of respiratory compromise and aspiration.
Diagnosis of Myasthenia gravis
- Best next step in diagnosis: Acetylcholine receptor antibody
- Anti-MuSK antibodies may be checked if anti-AChR is negative
- Bedside: Edrophonium (Tensilon test) is an anticholinesterase inhibitor that can be used as a diagnostic tool, ice pack test over the eyelids may improve symptoms
- An abnormal single-fiber EMG and/or a decremental response to repetitive nerve stimulation is the most confirmatory test.
- CT scan of the chest is used to evaluate for thymoma.
- Also, check for thyroid function test
Differential diagnosis of Myasthenia gravis
- Lambert eaton myasthenic syndrome
- Anticholinesterase inhibitors (eg. pyridostigmine)
- Prednisone, other immunosuppressants (eg, azathioprine, cyclosporine, mycophenolate mofetil)
- Plasmapheresis or IVIG can also be used for acute treatment.
- Surgical :Thymectomy