Address for
Correspondence: Dr. MC Rajesh MD, MBA, Senior Consultant
Anaesthesiologist, Baby Memorial Hospital, Kozhikode, Kerala,
India. PIN: 673004. E- mail: rithraj2@yahoo.co.in
Keywords: myasthenia gravis, spinal anaesthesia,
caesarian section
Introduction
Myasthenia gravis is an autoimmune disease affecting the neuro
muscuar junction, the pathology of which is known to be the
presence of auto antibodies directed against the Acetyl
Choline receptors which essentially destroys it. Anasthesia in
the affected is a challenge irrespective of pre existing
weakness as there is always a risk of peri operative
exacerbation. In this case report we present the case of a
young female who had been administered with subarachanoid
block for lower segment Cesarean section and had an uneventful
outcome.
Case report
A young female of second gravida (G2A1) who is a known case of
Myasthenia Gravis with no other co-morbidities presented to
the Pre-Anesthetic checkup clinic for elective Lower Segment
Caesarian Section (LSCS). She was diagnosed with Myasthenia
Gravis at 17 years of age when she first noticed weakness of
both lower limbs while climbing stairs. A year later, she
underwent Thymectomy as a curative management but episodes of
weakness continued to occur and she was started on
Physostigmine. The dose of the drug was gradually tapered over
the last 14 years. She has had an episode of Ptosis (ocular
involvement) but no episodes of respiratory distress till the
present day. Thymectomy was done under general anesthesia
which was uneventful. She has had a spontaneous complete
abortion one and half years back at less than 6 weeks of
gestation which did not require any further medical
intervention.
After confirming the present pregnancy, the dose of
Physostigmine was reduced to 60mg 8th hourly in the 1st
trimester (from 60 mg 6th hourly). The dose was increased back
to 60mg 6th hourly after 20 weeks of gestation. Apart from
short episodes of muscle weakness when skipping the dose of
the drug, she was completely asymptomatic during the present
pregnancy.
On examination, patient was conscious and oriented with no
significant clinical findings. She had a Heart Rate of 67
beats/minute, Blood Pressure of 118/75mm Hg and a SpO2 of 100%
in room air. Neurological examination revealed no significant
abnormalities. Other organ systems were within normal limits.
All the preoperative investigations were within normal limits
including a normal Thyroid Function Test.
The patient was premedicated with Inj. Ranitidine 50mg and
Inj. Metoclopramide 10mg 30 minute prior to the induction of
anesthesia. In the operating room, she was monitored with 5
lead ECG, SpO2 and Non Invasive Blood Pressure. Under strict
aseptic precautions, a subarachnoid block was performed with a
25G Quincke's needle with 7.5 mg Hyperbaric Bupivacaine and
25mcg Fentanyl at L3-L4 interspace. The anesthesia level was
assessed and was recorded to be at T6 level. Patient was given
10 IU of Oxytocin as infusion after the delivery of the baby.
Surgery lasted for 25 minutes and was uneventful. The level of
anesthesia was rechecked after the surgery and was recorded to
be at T6 level.
Patient was shifted to the post anesthesia care unit and post
operative analgesia was given with Inj. Paracetamol 1g IV 8
hourly and Inj. Tramadol 50mg IV 8 hourly. The regular dose of
Physostigmine was given 2 hours after the surgery. The levels
of anesthesia were checked every 2 hourly which revealed a
regression of three dermatome levels every 2 hours. She was
closely monitored for any muscle weakness or respiratory
distress in the post anesthesia care unit for 24 hours and
then was shifted to room. She was discharged on the 5th post
operative day without any significant complaints
Discussion
Myasthenia gravis is a rare disorder affecting the
Neuromuscular junction where Auto Antibodies cause destruction
of Nicotinic Acetyl Choline receptors. Muscle Specific Kinase
(MuSK) and the Low-density Lipoprotein receptor-related
protein (LRP4) are also identified as targets in some patients
[1]. Many cases are seen associated with abnormal cell
proliferations in the Thymus. But other factors like influence
of a pro inflammatory environment, genetic factors, sex
hormones and environmental factors are also implicated as
possible etiologies of Myasthenia [1].
Myasthenia is characterized by muscle weakness which usually
begins with Ocular symptoms like Ptosis, Diplopia and then
spread to other muscle groups [2]. This weakness usually
worsens with exertion and returns to normal on rest, and
periods of exacerbations occur multiple times during the
course of the disease [2]. In severe disease, oropharyngeal
and respiratory muscles may be involved, affecting speech,
chewing and swallowing thereby making the patients prone to
pulmonary aspiration and ventilatory support [2,6].
Hyperthyroidism, Hashimoto's disease, SLE, Rheumatoid
Arthritis, Red Cell Aplasia, Alopecia, Myocarditis, Conduction
defects, Takotsubo cardiomyopathy and Autnomic dysfunction
leading to hemodynamic disturbances may be seen in these
patients [2,7]. Diagnosis is usually established using
clinical features but as many as 20 diagnostic tests with
variable accuracy are available of which Anti Acetyl Choline
Receptor Antibody testing and Single Fiber EMG are of the
better quality than others [8]. Thymomas or Thymic hyperplasia
can be seen associated with these patients and Thymectomy
along with post operative regimen of Pyridostigmine and
Prednisolone is found to improve the clinical course in most
of these patients [3,4]. Other treatment modalities include
Immunomodulators like Steroids, Azathioprine,
Tacrolimus,Cyclosporine but IVIG and Plasmapheresis may be
needed for rapid response [9]. Oropharyngeal and respiratory
muscle involvement may warrant mechanical ventilatory support.
Myasthenia and pregnancy is a dangerous combination as
myasthenia is a potent risk factor complicating pregnancy [3],
the labour, the postpartum period, as well as the the neonate
while pregnancy can result in deterioration of myasthenia
which may even warrant mechanical ventilator support [4].
Exacerbation of myasthenia has to be anticipated in all
pregnant patients as it may occur even in Thymectomised
patients and there are no risk assessment criteria for the
same.
A review of literature shows women with Myasthenia can go
through the pregnancy without any significant issues and only
about one third of the patients suffer exacerbations [10]. A
planned pregnancy should always be preferred when the disease
is stable and it is advisable to avoid pregnancy at the
beginning of the disease [11]. Just as in our case, most
patients can be managed with Anticholinesterases but some may
require additional therapies like Steroids, Immunomodulators,
IVIG or even Plasmapheresis depending on the severity [12].
Most exacerbations are seen in the first trimester and post
partum period and most of them can be controlled by dose
adjustment of Anticholinesterases alone [12]. Due to the high
prevalence of multiple co-existing illnesses, a thorough
workup including evaluation by Neurologists, Cardiologists,
Rheumatologists and Endocrinologists are often necessary apart
from an expert Obstetric care.
Myasthenia gravis as such is not an indication for Caesarian
Section but many Obstetricians avoid vaginal delivery because
of the fear of a prolonged labour and associated muscle
tiredness of the patient [14]. Second stage of labour may also
be complicated by an acute respiratory difficulty which may
need mechanical ventilatory support [14]. This warrants a
preoperative anesthetic evaluation and a tertiary care setup
with a pre arranged emergency operation theatre if the
Obstetrician plans a normal vaginal delivery. Epidural
analgesia maybe indicated to alleviate labour pain but it
carries the extra risk of prolonging labour which may prove
detrimental to the patient. Obstetric complications are
uncommon in Myasthenia and Caesarian Section may be required
if any occur [13].
Caesarian section poses unique challenges to the
Anesthesiologist as both general anesthesia and regional
anesthesia are associated with complications in a myasthenic
patient. A review of literature shows caesarian section has
been performed successfully with both general anesthesia and
regional anesthesia but complications including severe
respiratory compromise needing post operative ventilation and
ICU admission was required in some patients, indicating that
no method is superior over the other. Bulbar involvement or
respiratory compromise is the only true indication for general
anesthesia in these patients. Although most intravenous and
inhalational agents can be safely used in Myasthenic patients,
use of muscle relaxants should be as limited as possible.
Succinyl choline may produce unpredictable responses and hence
is better avoided, while non depolarizing muscle relaxants
should be administered cautiously using neuromuscular
monitoring [15]. Delayed emergence, residual muscle paralysis
and respiratory failure needing prolonged ventilatory support
has been reported [15] which adds to the list of problems
pregnancy itself causes while administering general
anesthesia.
Many authors are seen to prefer Regional anesthesia; spinal,
epidural and combined spinal epidural could all be used, each
with their own risks and benefits. Sanwal MK et al [10]
reports a case of Caesarian section in a Myasthenic patient
managed with spinal anesthesia using low dose Bupivacaine and
short acting Opioid without any significant complications. The
combination of Opioid helps to reduce the dose of local
anesthetic and also reduce the motor blockade. However,
Almeida C et al [15] reports an incidence of dyspnea requiring
mechanical ventilation following the administration of
Subarachnoid block. Thus, low dose spinal anesthesia with
careful monitoring of level of the block and patient
respiratory efforts can also be a method of anesthesia for
caesarian section in myasthenic patients. Continuous Epidural
anesthesia with local anesthetics and opioid can also be
another alternative but since epidural anesthesia require
large amounts of local anesthetics, they may interfere with
neuromuscular transmission in myasthenic patients [15].
Conclusion
Myasthenia gravis has an unpredictable course during
pregnancy, thereby producing serious management challenges to
the obstetrician and anaesthesiologist. Caesarian section if
indicated in such patients poses unique challenges to the
anesthesiologist as all available modes of anesthesia are
associated with its own risks and benefits.
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