Myasthenia gravis
- Autoantibodies bind to Ach receptors at the post-synaptic membrane of the NMJ
- More common in women
- Tends to present younger in women and later in men
- Characterised by;
- Muscle weakness
- Fatiguability
- Improvement after rest
- Muscle weakness
- Muscles affected (most common – least common)
- Extraocular resulting in double vision and ptosis
- Bulbar leading to difficulty chewing, swallowing and talking
- Neck, difficulty lifting the neck up from lying position
- Proximal limb, difficulty lifting arms above shoulder level
- Trunk, breathing problems and difficulty sitting from lying position
- Distal limbs, weak hand grips, ankles and feet
- Extraocular resulting in double vision and ptosis
Investigation
- Tensilon test
- Edrophonium chloride, a short acting acetylcholinesterase inhibitor
- Produces transient alleviation of symptoms
- May induce bradycardia (requires atropine)
- Edrophonium chloride, a short acting acetylcholinesterase inhibitor
- Detection of serum acetylcholine receptor antibodies
- EMG studies
- Chest radiography and CT of mediastium to demonstrate enlargement of thymus
- 10-15% of patients have thymoma
- 50% have thymic hyperplasia
- 10-15% of patients have thymoma
Management
- Anticholinesterase drugs
- Immunosuppression
- Steroids
- Steroid sparing drugs;
- Azathioprine
- Methotrexate
- Azathioprine
- Steroids
- Thymectomy
- Plasma exchange or I.V. immunoglobulins for seriously weak patients
- A severely weak patient may be due to;
- Under treatment with aceylcholinesterase inhibitors
- Over treatment resulting in excessive Ach resulting in depolarising blockade
- Under treatment with aceylcholinesterase inhibitors