Succinylcholine is given to a patient and the anaesthetist observes that instead of the typical brief fasciculations and paralysis, the patient shows prolonged paralysis for 45 minutes. Which enzyme deficiency best explains this?

• A Acetylcholinesterase deficiency
• B Adenylate kinase deficiency
• C Malate dehydrogenase deficiency
• D Plasma pseudocholinesterase (butyrylcholinesterase) deficiency ✓

Explanation

Succinylcholine is normally rapidly hydrolysed by plasma pseudocholinesterase (butyrylcholinesterase) within 5–10 minutes. Dibucaine-resistant variants (dibucaine number <30 vs normal >70) indicate the atypical enzyme with markedly reduced succinylcholine hydrolysis, leading to 'scoline apnoea' lasting 2–6 hours. The dibucaine number measures percentage inhibition of the enzyme by dibucaine — normal is 70–80. Acetylcholinesterase at the neuromuscular junction does not hydrolyse succinylcholine. Treatment is supportive with continued mechanical ventilation until spontaneous recovery.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.