ICU · Neurocritical care / neuromuscular

Myasthenia Gravis & Myasthenic Crisis — NMJ Weakness, PLEX/IVIG & Steroid Exacerbation

Also known as Myasthenia gravis · MG · Myasthenic crisis · Cholinergic crisis · Acetylcholine receptor antibody · AChR antibody · MuSK antibody · Pyridostigmine · Plasma exchange · Thymoma · Neuromuscular junction · Fatigable weakness

Myasthenia gravis (MG) is an autoimmune disease of the post-synaptic acetylcholine receptor at the neuromuscular junction — the acetylcholine receptor antibodies damage the receptors, causing a fatigable weakness (worse with the activity, better with the rest). The ocular (the ptosis, the diplopia), the bulbar, and the limb muscles are affected; the reflexes and the sensation are PRESERVED (a key discriminator from the Guillain-Barre). The myasthenic crisis is the life-threatening respiratory or the bulbar failure, precipitated by the infection, the surgery, or the junction-worsening drugs. The management: intubate early on the falling serial spirometry and the bulbar failure (the trend and the pronounced bulbar weakness decide before the hypercapnia does); the plasma exchange OR the IVIG (equivalent in the randomised head-to-head trials); the high-dose corticosteroid COMBINED with the exchange or the immunoglobulin as the cornerstone in the established crisis; stop every drug that may be worsening the junction. The cholinergic crisis (the excess pyridostigmine) causes the weakness PLUS the cholinergic overdrive (the miosis, the salivation, the bradycardia, the sweating) — wet vs the dry myasthenic crisis. Screen for the thymoma (the chest CT); the thymectomy if the thymoma.