Myasthenia Gravis Presenting as Isolated Respiratory Failure: A Case Report

Abstract

Myasthenia gravis (MG) is often complicated by respiratory failure, known as a myasthenic crisis. However, most of the patients who develop respiratory symptoms do so during the late course of disease and have other neurological signs and symptoms. However, in some patients respiratory failure is the initial presenting symptom. We report the case of a 68-year-old woman with MG who presented with isolated respiratory failure as her first presenting symptom. As illustrated by this case, it is important to consider neuromuscular disorders in cases of unexplained respiratory failure.

Full text

Myasthenia Gravis Presenting as Isolated Respiratory
Failure: A Case Report
Won Hee Kim1, Jung Hyun Kim1, Eun Kyung Kim1, Sang Pil Yun1, Kyung Keun Kim2, Won Chan Kim2,
and Hye Cheol Jeong1
Division of Respiratory and Critical Care Medicine, Departments of 1Internal Medicine and 2Neurology, CHA Bundang
Medical Center, CHA University School of Medicine, Seongnam, Korea
DOI: 10.3904/kjim.2010.25.1.101
CASE REPORT
Myasthenia gravis (MG) is often complicated by respiratory failure, known as a myasthenic crisis. However,
most of the patients who develop respiratory symptoms do so during the late course of disease and have other
neurological signs and symptoms. However, in some patients respiratory failure is the initial presenting symptom.
We report the case of a 68-year-old woman with MG who presented with isolated respiratory failure as her first
presenting symptom. As illustrated by this case, it is important to consider neuromuscular disorders in cases of
unexplained respiratory failure. (Korean J Intern Med 2010;25:101-104)
Keywords: Myasthenia gravis; Respiratory insufficiency
Received: June 29, 2007
Accepted: September 21, 2007
Correspondence to Hye Cheol Jeong, M.D.
Division of Respiratory and Critical Care Medicine, Department of Internal Medicine, CHA Bundang Medical Center, CHA University School of
Medicine, 351 Yatap-dong, Bundang-gu, Seongnam 463-712, Korea
Tel: 82-31-780-6142, Fax: 82-31-780-4800, E-mail: jhcmd@hanmail.net
INTRODUCTION
Myasthenia gravis (MG) is a chronic autoimmune
neuromuscular disease. MG is characterized by autoanti-
body attack of acetylcholine receptors at the motor end
plate of striated muscles, which results in variable muscle
weakness made worse by exercise [1]. Patients with MG
commonly experience respiratory failure. However, most
patients have respiratory failure during the late course of
MG and usually have additional neurological symptoms.
We treated a woman with MG who presented with isolated
respiratory failure as the first symptom of MG. Here we
report this case.
CASE REPORT
A 68-year-old woman presented to the emergency
department with dyspnea for one week. She denied a
cough, sputum, chest pain or other respiratory symptoms.
She also denied symptoms of upper and lower extremity
weakness, blurred vision or swallowing difficulty. Sixteen
years previously, she was diagnosed with diabetes mellitus,
hypertension and depression. Eleven years ago, she under-
went total thyroidectomy for a papillary thyroid carcinoma.
The patient was taking selective serotonin reuptake inhibitor,
zolpidem, alprazolam and methylphenidate for insomnia
and depression, levothyroxin and alfacalcidol for thyroid
disease, a calcium channel blocker for hyper-tension, and
sulfonylurea and metformin for type 2 diabetes mellitus.
On the initial physical examination, the patient was not
in acute respiratory distress. The vital signs were normal:
blood pressure was 170/90 mmHg, pulse rate was 92
beats/min, respiratory rate was 24 breaths/min, and body
temperature was 36˚C. The mental status was intact, the
patient was alert and the neurological examinations of
cerebral function, cerebellar function and both extremities
were normal. Pretibial pitting edema and neck vein
engorgement were absent. On the chest auscultation,
there were mild crackles at both lower lung fields. The
body mass index was 24.2 kg/m2.
The laboratory evaluation showed a white blood cell

count of 6,580/µL, hemoglobin of 12.0 g/dL and platelet
count of 325,000/µL. Other blood chemistries were
within normal limits: BUN/Cr 12.2/0.9 mg/dL, AST/ALT
25/25 units/L, NT-proBNP 107.2 pg/mL, and glucose 92
mg/dL. Thyroid function testing showed: T3 0.73 ng/mL,
FT4 1.71 ng/dL and TSH < 0.003 µIU/mL. The arterial
blood gas analysis, on room air, was pH 7.441, PaCO2 39.9
mmHg, PaO2 64.7 mmHg, oxygen saturation 93.2%, and
D(A-a)O2 36.
The initial chest X-ray showed a slightly reduced lung
volume (Fig. 1A). The chest computed tomography (CT)
scan showed no evidence of pulmonary thromboembolism,
but there was bibasilar atelectasis (Fig. 2). Echocardiography
revealed normal systolic and diastolic heart function.
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Figure 1. Plain chest radiography. (A) On the first day of the hospital admission, the chest X-ray revealed normal findings except for a
focal atelectasis in the right middle lung field. (B) On the sixth day, the chest X-ray showed reduced lung volume.
A B
Figure 2. Spiral computed tomography (CT) scan of the chest. (A) CT scan shows multifocal atelectasis in both lungs. (B) There was
no definite evidence of an acute pulmonary thromboembolism.
A B

During the next five days, her dyspnea became more
severe. On the sixth day of hospitalization, the patient had
severe respiratory distress with labored breathing. The
respiratory rate was 40 breaths/min and the mental status
was confused. The arterial blood gas analysis on an O2
mask with 10 L was pH 7.324, PaCO2 54.9 mmHg, PaO2
94.4 mmHg, and oxygen saturation 96.6%. The chest X-
ray revealed no definite infiltration but the lung volume
was reduced (Fig. 1B). The patient was transferred to the
intensive care unit and mechanically ventilated.
We considered other causes of respiratory failure such
as neuromuscular disorders, Guillain-Barre syndrome or
myasthenia gravis. The physical and neurological exami-
nation and cerebrospinal fluid analysis were normal. A
diagnosis of MG was made based on the neurophysiological
studies. The electromyography showed a decrement in
response to repetitive nerve stimulation in various
muscles (Fig. 3). The pharmacological Jolly test revealed
incremental responses of tidal volume of ventilation (Fig.
4). The repeated acetylcholine antibody titers were 8.9
nmol/L and 12.4 nmol/L.
Pyridostigmine bromide, 720 mg/day and prednisolone,
30 mg/day was prescribed and intravenous gamma-
globulin, 27 g/day for 5 days were administered. Weaning
from the ventilator failed over the next 2 weeks; therefore,
a tracheostomy was performed. However, the patient was
eventually successfully weaned from the ventilator and 2
months later, she was discharged.
DISCUSSION
MG is an autoimmune disorder. In about two thirds of
patients, extrinsic ocular muscle abnormalities present as
the initial symptoms or bulbar weakness may also be the
initial symptoms. The symptoms usually progress to
include the limb muscles [1]. Respiratory failure can be a
complication during the late course of MG in about 3 to
8% of cases, known as a myasthenic crisis [2]. However,
isolated respiratory failure as the presenting symptom, as
in the present case, is very unusual and this patient is the
Kim WH, et al. Mysthenia gravis presenting as isolated respiratory failure
103
Figure 3. Electromyography of abductor digiti minimi and orbicularis oculi muscle. (A) These findings demonstrate a decrement in
the compound muscle action potential amplitude of about 20% at 2 Hz stimulation at the abductor digiti minimi muscle and (B) more
than 70% at 5 Hz stimulation at orbicularis oculi muscle.
A B
2 mV
Aductor digiti minimi Orbicularis oculi
5 ms 200 uV 2 ms
Figure 4. The neostigmine test. The patient was on mechanical
ventilation; we evaluated the tidal volume after the intra-
muscular injection of neostigmine. After the neostigmine 10 mg
injection, the tidal volume increased from 200 mL/min to 280
mL/min (Servo I, Maquet Medical, Solna, Sweden).

first case reported in Korea.
Recently, several cases of MG with respiratory failure as
a first manifestation have been reported [3-6]. In these
studies, respiratory failure as an initial symptom was
observed in 14 to 18% of the patients. Most of the patients
presented with ocular and bulbar muscle involvement [7].
However, our patient showed no other neurological
symptoms associated with MG. Therefore, we did not
suspect MG initially. We tried to determine the cause of
the respiratory failure. We did not find any evidence of a
hypoxemic respiratory failure; there were no definite
infiltrations, edema, effusion or pneumothorax on chest
X-ray. There was no evidence of pulmonary thromboem-
bolism on the chest CT scan and no evidence of intracardiac
shunting or congestive heart failure on the echocardiography.
Therefore, we suspected an acute ventilatory failure.
Drugs or trauma that could cause ventilatory failure was
ruled out. The electrolyte levels were within normal limits.
Based on these results, we investigated the possibility of a
neuromuscular disease, especially Guillain-Barre syndrome
and myasthenia gravis, the most common and the second
most common cause of neuromuscular disease, respectively.
However, the cerebrospinal fluid was normal, and the
neurophysiological studies showed evidence of myasthenia
gravis.
Generally patients with neuromuscular disease present
with hypoxia and a normal D(A-a)O2 due to hypoventilation,
but in the present patient there was an increased D(A-
a)O2. Patients with MG occasionally have atelectasis [8],
which could result in this finding.
The patient had negative results on multiple tests for the
evaluation of respiratory failure. It is difficult to consider a
neuromuscular disorder, especially myasthenia gravis,
unless there are other neurological symptoms such as
ocular or bulbar symptoms. Unlike previous cases, our
patient presented with only respiratory symptoms, the
patient had no other symptoms generally associated with
MG during her 6-month follow-up visits.
We report the case of a 68-year-old woman who
presented with respiratory failure as the only symptom of
myasthenia gravis. As seen in this case, MG can manifest
as isolated respiratory failure. Therefore, one should
consider neuromuscular disorders in cases of unexplained
respiratory failure.
Conflict of interest
No potential conflict of interest relevant to this article
was reported.
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