Myasthenia Gravis
Introduction
Myasthenia gravis is an autoimmune disease that attacks the connections between nerves and muscles, resulting in weakness in skeletal muscles (e.g. muscles that control the eyes, face, neck and limbs).
- In most cases, the immune system targets the acetylcholine (ACh) receptor (less commonly the muscle-specific tyrosine kinase MuSK).
- Most often in females aged 10 to 30 years and males aged 50 to 70 years.
Symptoms often include changes to the eyes/vision [e.g., double vision (diplopia), drooping eyelid (ptosis)], problems with chewing/swallowing and weakness in the neck and jaw.
Management
Cholinesterase inhibitors (specifically pyridostigmine) are the mainstay of treatment in myasthenia gravis, especially in ocular disease or mild generalized disease.
- Time the doses for when the patient is most fatigued (e.g. 30 to 45 minutes before meals when the patient has bulbar weakness).
- Cholinergic effects can occur, e.g. salivation, lacrimation, excessive urination, diarrhoea.
For more severe disease or when acetylcholinesterase inhibitors are inadequate, the next step is immunosuppressive medication.
- Oral corticosteroids (e.g. prednisolone) should be the first-choice drug.
- May also be used to provide short-term benefit.
- An uncommon effect of starting a high corticosteroid dose is that symptoms can get worse in the first 3 to 7 days, but this is transient.
- Azathioprine, cyclosporine or mycophenolate mofetil may be effective but have risks of severe adverse effects.
Biologics that can be considered for generalized myasthenia gravis include
- Eculizumab
- Ravulizumab
- Zilucoplan
- Efgartigimod
- Rozanolixizumab
- Rituximab (off-label second-line option)
Some severe cases require treatment with plasmapheresis or intravenous immunoglobulin (IVIG), or even thymectomy (removal of the thymus gland - recommended for patients with thymoma).
Drugs to Avoid or Use with Caution
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