The perianaesthetic management of a patient with myasthenia gravis

Sir,

A vaginal hysterectomy was planned for a 54-year-old woman, weighing 80 kg with a body mass index (BMI) of 33, who had complaints of abnormal uterine bleeding. She complained of intermittent lower back pain for which she was advised magnetic resonance imaging (MRI) of lumbo-sacral spine, which showed a 2 × 4 cm intraspinal cystic lesion of cerebrospinal fluid intensity extending from first (L1) lumbar to fourth (L4) lumbar level. She did not provide any history of previous surgery or anaesthesia exposure and had good effort tolerance. Pre-anesthesia check up (PAC) fitness was given with routine preoperative orders.

In our institute, we follow a two tier system, where after preliminary PAC by a resident, it is reviewed by a consultant anaesthetist next day prior to surgery. This second checkpoint helps to review the PAC and check consent documentation after proper patient identification. This practice at times is beneficial, as described in the present case, where on review it was found that the patient had been reluctant in sharing medical history. This prompted the anaesthetist to closely scrutinise the history of past medical illness and seek elaborate details revealing that the patient had suffered from myasthenia gravis (MG) 5 years ago. She had received treatment for 4 years and was asymptomatic for the last year and since all medications were stopped. The patient felt that since she had been cured of the illness she did not need to disclose it. We discussed the same with the surgeon but considering the semi-emergency of a bleeding patient we took a combined decision to proceed, but with a written consent of the patient and the relatives, reflecting the risk of morbidity associated, i.e., the risk of postoperative prolonged ventilatory support in intensive care unit (ICU).

Regional anesthesia is preferred in MG considering the pathophysiology of the disease. However, since our patient had a collection in lumbar area, indicating a possible infection, central neuraxial block was contraindicated. Therefore, general anaesthesia was the only option left for us. After attaching monitors and obtaining intravenous access, fentanyl injection (1.5 μg/kg) was administered. Inj. propofol 1.5 mg/kg, sevoflurane 2.5% with oxygen were given after pre-oxygenation. After additional 30mg propofol bolus, laryngoscopy was attempted and endotracheal intubation was done with ease and anaesthesia was maintained with 50% O₂ and 50% N₂O along with sevoflurane 2.5% with intermittent boluses of propofol as per vitals. Toward the end of surgery (1.5 hours), inhalational agents were discontinued and patient was safely extubated after being fully awake and confirming adequate respiratory efforts. She was monitored in recovery for 1 hour and then in ICU for 24 hours. She remained well and was discharged on 3^rd day after neurological consultation.

Anaesthesia risks for a MG patient are well described in the literature. It affects the neuromuscular junction (NMJ) and its interaction with anaesthesia drugs, especially neuromuscular blocking drugs (NMBDs) poses a challenge for the anaesthetist. Therefore, regional anaesthesia is preferred to avoid postoperative respiratory depression and delayed recovery due to sensitivity to muscle relaxants.[1] Auto-antibodies develop against acetylcholine nicotinic postsynaptic receptors (AChR). Patients become symptomatic once receptors are reduced to 30% of normal. Antibodies reduce the number of functional receptors by increasing their degradation via complement-induced damage to NMJ. Antibodies are detected in sera of 85-90% MG cases. Cured MG must be assumed to be in active phase. The concept of cured is not valid in MG as functional receptor population is reduced/depleted. Muscle weakness becomes apparent when >70% AchR are blocked but in MG this “margin of safety,” i.e., presence of excess of receptors is reduced. Case reports have reported safe use of intermediate acting muscle relaxants (10-50% dose reduction).

Though the patients may be symptom-free and in remission, they are sensitive to neuromuscular blocking drugs (NMBDs) as per one case report.[2] Due to non-availability of sugammadex, we avoided using non-depolarising NMBDs. MG cases are unpredictably resistant to depolarising NMBDs and unpredictably sensitive to non-depolarising NMBDs.[3] Hence, a MG patient, despite being in remission or cured, must be considered active, with planned anaesthesia according to surgery being vital to reduce morbidities.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient has given her consent for her images and other clinical information to be reported in the journal. The patient understands that her name and initials will not be published and due efforts will be made to conceal identity, but anonymity cannot be guaranteed.

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Conflicts of interest

There are no conflicts of interest.