Myasthenia Gravis

• General: Autoimmune disease caused by antibodies to acetylcholine receptors in the neuromuscular junction
• Clinical:
• usually affects proximal muscles, neck extensors, facial/bulbar muscles (ptosis, diplopia, dysphagia, dysarthria)
• usually no sensory or DTR deficit
• associated with thymoma or thymic hyperplasia
• Myasthenia Crisis: respiratory failure precipiated by infection vs. surgery vs. rapid taper in medication; may require intubation (be mindful of paralytic)
• Diagnosis:
• applying ice to ptosis (should improve)
• administering edrophonium (anticholinesterase inhibitor) which should improve muscle weakness
• acetylcholine receptor antibodies levels
• EMG

• Management:
• assess respiratory function: VC < 1L; NIF < 20; weak cough; bulbar weakness
• plasma exchange or IVIG
• consult neurology and admit the patient to the ICU
• acetylcholinesterase inhibitors (pyridostigmine, neostigmine)
• thymectomy
• immunosuppression with steroids and immunosuppressant
• Medications that can exacerbate symptoms: fluoroquinolones, macrolides, aminoglycosides, paralytics, magnesium, penicillamine

Lambert-Eaton Syndrome

• General: Autoimmune disorder caused by antibodies to voltage gated calcium channel in NMJ, preventing Acetylcholine release
• Clinical:
• affects proximal muscles, lower extremity more so than upper extremity
• can have autonomic symptoms: dry mouth, constipation, erectile dysfunction
• associated with small cell lung cancer
• rarely results in respiratory or bulbar failure
• Diagnosis: VGCC antibodies; repetitive nerve testing
  
• Management:
• 3,4-Diaminopyridine is first line
• Steroids or IVIG
• plasma exchange
• search for underlying malignancy