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Masseter muscle rigidity (MMR), the so-called “jaw of steel,” is a significant stiffness of the jaw leading to almost impossible laryngoscopy. MMR is a rare complication of succinylcholine administration during general anesthesia in healthy persons; however, it is more common in patients with muscle disease such as malignant hyperthermia (MH) and myotonia. We report a case here of the use of a higher dose of propofol to break down succinylcholine-induced MMR and general sustained muscle rigidity in a patient with paramyotonia congenita (PC).
A 40-year-old female (weight = 78 kg and height = 157 cm), with a known past medical history of hepatitis B, gastroesophageal reflux disease (GERD), anxiety, tobacco abuse, and remote methamphetamine abuse, was scheduled to undergo a laparoscopic cystectomy and salpingo-oophorectomy at our ambulatory surgical center. Before her scheduled operation, the patient underwent evaluation at our anesthesia preoperative clinic. Her airway exam demonstrated Mallampati score 2, full range of motion for her neck and more than 3 finger-breath thyromental distance. She had a documented allergy to sulfamethoxazole-trimethoprim. On the day of surgery, she was very anxious and reported slight nausea. With this history, in addition to the history of GERD, a rapid sequence induction was planned. She was premedicated with 4 mg of midazolam intravenously (IV). General anesthesia induction commenced with IV bolus of 50 µg of fentanyl and concurrent administration of 50 mg of IV lidocaine and 200 mg IV propofol. This was followed by 100 mg IV succinylcholine. Immediately after administration of succinylcholine, she developed significant muscle rigidity of bilateral upper extremities, neck, and most notably her masseter muscles. With the inability to open the patient's mouth, positive pressure ventilation was applied and held with immediate dosing of an additional 100 mg IV propofol. Mask ventilation with good air exchange was possible and carried out. After ~4–5 min, both arms, jaw, and other contracted muscles relaxed, and the patient was successfully intubated without difficulty. The patient's vital signs remained stable throughout events. Her end-tidal CO2, minute ventilation, and temperature were monitored vigilantly and remained stable. After successful intubation, total IV anesthesia with propofol infusion and, as needed, fentanyl and rocuronium boluses were initiated and no further inhalational agents were given. The anesthesia circuit and CO2 absorbent were changed and flushed. Vaporizers were taken off of the anesthesia machine. No additional muscle rigidity noted throughout the remainder of case and the rest of the case was uneventful. The patient was discharged home later that day. Postoperatively, the patient was seen by the neurology service and was diagnosed with PC.
PC is a rare (<1:100,000) autosomal dominant disease of skeletal muscles involving a mutation of a gene on chromosome 17q affecting the sodium membrane channels in the skeletal muscle cell membrane. Patients with PC experience episodes of sustained myotonia or generalized muscular contraction and rigidity, commonly induced by exercise, muscle cooling, or drugs such as succinylcholine; therefore, these conditions and drugs should be avoided in these patients. PC is not associated with MH, even though its presentation after succinylcholine administration has been misdiagnosed as an early sign of MH. It is known from clinical experience that propofol relaxes skeletal muscles. The mechanism by which propofol reduces muscle tone and causes muscle relaxation is not fully understood. Haeseler et al. studied the effect of propofol on the human muscle sodium channels in vitro. They found that propofol blocks these channels in a voltage-dependent manner. In a different study, Haeseler et al. investigated the propofol action on the mutant sodium channels in cells taken from a patient with PC. Their study revealed that propofol can modulate gating in the mutant sodium channels which may lead to decrease the enhanced muscle excitability in these patients. Ummenhofer et al. showed that propofol decreases the succinylcholine-induced increase of masseter tone in a clinical trial. Their study suggested that without the use of a defasciculating dose of a nondepolarizing neuromuscular blocking drug, propofol, compared with thiopentone, had provided better conditions for tracheal intubation with respect to a succinylcholine-dependent increase in jaw tension. To the best of our knowledge, our case report is the first to show that using a higher dose of propofol may help reduce succinylcholine-induced muscle rigidity in a patient with PC. In vitro studies showed that propofol worked on both normal and abnormal membrane sodium channels.[4,5] Our case suggests that high dose of propofol could be the best and safest option to treat MMR cases even in patients with muscle disease.
There are no conflicts of interest.