Disease | Presentation | Diagnostics | Treatment |
- Weakness – Symmetrical – Primarily proximal - Usually occurs days/weeks after respiratory/gastrointestinal infection (Campylobacter jejuni) | 1. Lumbar puncture: increased protein in CSF 2. NCV: decreased | 1. Plasmapheresis 2. Immunoglobulin therapy | |
- Weakness is worse at the end of the day - Commonly affects eyes (ophthalmoplegia/ptosis/diplopia), face, and swallowing ability | 1. Chest X-ray: rule out thymoma 2. Tensilon test(edrophonium: no longer popular as it may cause life-threatening bradycardia): positive if muscles get stronger with Tensilon 3. Nerve conduction study/EMG 4. Antibodies against the muscle receptor for acetylcholine | 1. Acetylcholinesterase inhibitors (pyridostigmine/neostigmine) 2. Immunosuppressants 3. Removal of thymus 4. Plasmapheresis 5. IV immunoglobulin (in crisis) | |
Lambert–Eaton Myasthenic Syndrome (LEMS) | - Weakness – Improves with activity – primarily proximal - Dysfunction of autonomic system (dry mouth/constipation/blurred vision) - Usually occurs in the setting of paraneoplastic syndrome (frequently small cell lung cancer) - Starts at extremities and moves up | 1. EMG/NCV (compound motor action potentials and single-fiber examination) 2. Antibodies against pre-synaptic voltage-gated calcium channels (the nerve where acetylcholine is released) 3. CT to find the cancer (small cell lung). If negative, may have to be repeated within a few months. Consider bronchoscopy and PET | 1. Treat cancer 2. Steroids 3. Immunosuppressants 4. Aminopyridines |
- A myasthenic snarl (or transverse smile) may be seen with bulbar muscle involvement in myasthenia gravis
- EMG test
- LEMS
- ≥60% increment at high-rate stimulation or postexercise facilitation
- MG
- Decrement at low-rate stimulation (LRS)
- How does one administer a Tensilon test?
- 1mL of 1% edrophonium chloride (10 mg/mL, Tensilon) is prepared. The patient is given an initial dose of 0.1 mL and observed for a response. If the patient’s symptoms do not change, the remaining 0.9 mL is administered and the response observed again. Administration of an acetylcholinesterase (AChE) inhibitor, such as edrophonium, causes transient improvement in symptoms of myasthenia gravis.
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