A patient with myasthenia gravis undergoing thymectomy receives atracurium. Compared to a healthy patient, the expected sensitivity of this patient to atracurium is:

• A Decreased sensitivity; antibodies occupy receptors reducing block efficacy
• B Unchanged; atracurium acts independently of receptor number
• C Unpredictable; depends solely on acetylcholinesterase activity
• D Increased sensitivity; reduced receptor number requires lower doses ✓

Explanation

Myasthenia gravis results in autoimmune destruction of nicotinic acetylcholine receptors (NMJ), reducing the total receptor population. Non-depolarising muscle relaxants compete with acetylcholine for the remaining receptors; with fewer receptors available, a given dose of NDMR occupies a greater proportion of the total receptor pool, producing enhanced and prolonged block. Clinically, MG patients are markedly sensitive to NDMRs and require 10–50% of normal doses. In contrast, they are relatively resistant to succinylcholine (due to reduced receptor numbers) and require higher doses. Resistance to NDMRs is characteristic of motor neuron disease/denervation, not MG.

Reference: Morgan & Mikhail's Clinical Anesthesiology, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.