<Presentation of a
Case>
A 53 year-old woman with hypertension and mild right ptosis
since 2 years ago was admitted because of chronic cough with
occasional fever refractory to medications for 3 months prior
to entry. She was seen at a local hospital for progressive
dyspnea 2 months earlier. Because of worsening respiratory
distress, she was intubated and was admitted to intensive care
unit (ICU) then. She experienced several episodes of
extubation failure. Dysphagia and poor saliva swallowing have
been noted after successful extubation. Non-contrast brain CT
revealed no definite lesions. She was discharged later.
After discharge, dysphagia, poor oral intake, cough, and
much salivary secretion persisted, so she was brought to our
ER for help. An ENT specialist was consulted for suspected
oropharnygeal lesions. However, only much saliva pooling over
the vocal cord and pyriform sinus was noted. Respiratory
distress occurred during ENT examination and emergent
intubation was performed at ER. She was admitted to ICU for
further management.
On admission, physical examination
showed a woman of 164 cm in height and 50 kg in weight. Her
temperature was 36.6o
C,
blood pressure was 166/88 mmHg, pulse rate was 90 beats per
minute, and respiratory rate was 22 breaths per minute. Her
consciousness was clear. Her conjunctivae were pink, and the
sclerae were anicteric. The pupils were isocoric with prompt
light reflexes. The neck was supple without lymphadenopathy,
engorged jugular veins, palpable thyroid gland or carotid
bruits. The chest wall expansion was symmetric, and breath
sounds were bilaterally coarse. The heart beats were regular
without audible murmur. The abdomen was soft. Bowel sounds
were normoactive and liver and spleen were impalpable. Her
extremities were freely movable without edema, but the muscle
power was about 3~4 score over four extremities
symmetrically.
<Laboratory
Data>
CBC/DC:
WBC |
Hb |
Hct |
MCV |
Platelet |
Seg |
Eos |
K/μL |
g/dL |
% |
fL |
k/μL |
% |
% |
11.9 |
9.9 |
30.5 |
88.7 |
219 |
86.5 |
0.3 |
Baso |
Mon |
Lym |
ALB |
T-Bil |
AST |
ALT |
% |
% |
% |
g/dL |
mg/dL |
U/L |
U/L |
0.1 |
3.2 |
9.9 |
3.95 |
0.49 |
28 |
15 |
BUN |
Cr |
LDH |
Na |
K |
CRP |
Glucose |
mg/dL |
mg/dL |
U/L |
mmol/L |
mmol/L |
mg/dL |
mg/dL |
22.6 |
0.7 |
381 |
138 |
3.5 |
0.79 |
170 |
Urine
analysis:
Appearance |
Sp.Gr |
pH |
Protein |
Glucose |
Ketone |
OB |
|
|
|
mg/dL |
mg/dL |
|
|
Y, C |
1.03 |
6 |
300 |
- |
- |
1+ |
Urobilirubin |
Bilirubin |
Nitrate |
WBC |
RBC |
Epi |
Cast |
|
|
|
HPF |
HPF |
HPF |
|
+ |
- |
- |
2-5 |
2-4 |
0-2 |
0 |
<Course and
Treatment>
After admission, ampicillin-sulbactam was given for
suspected aspiration pneumonia. Ventilator weaning was
attempted and she was extubated. However, hypoventilation,
respiratory distress, tachycardia, and frequent VPCs were
noted after extubation. Re-intubation was performed soon.
Ptosis and proximal muscle weakness were more obvious after
extubation failure. Myasthenia gravis (MG) was suspected
according to clinical symptoms and signs. Antibody to
acetylcholine receptor was checked to reveal an elevated level
of antibody against acetylcholine receptor (18.131 nmol/L),
and myasthenic crisis was diagnosed. She underwent
plasmapheresis for 5 consecutive days followed by prednisolone
50 mg qd. Muscle power improved gradually. The maximal
pressure of inspiration (Pimax) improved from -40
cmH2O to -60 cmH2O, and the maximal
pressure of expiration (Pemax) improved from 26
cmH2O to 60 cmH2O. She was extubated
successfully without recurrent respiratory failure. Review of
her previous chest CT at another hospital revealed a soft
tissue density suggestive of thymoma.
<Discussion>
There are two clinical forms of myasthenia: ocular and
generalized. In ocular myasthenia gravis (MG), the weakness is
limited to the eyelids and extraocular muscles. In generalized
disease, the weakness also affects ocular muscles, but it may
involve a variable combination of bulbar, limb, and
respiratory muscles. About half of the patients with purely
ocular MG have positive antibody against acetylcholine
receptor, compared with nearly four-fifths of those with
generalized MG. About 10-15% MG patients have thymoma.
The cardinal feature of MG is fluctuating skeletal muscle
weakness, often with true muscle fatigue. The weakness may
fluctuate throughout the day, but it is most commonly worse
later in the day or evening, or after exercise. More than 50
percent of patients present with ptosis and/or diplopia.
Patients who present with ocular manifestations, about half
will develop generalized disease within two years. About 15
percent of patients present with bulbar symptoms, which
include dysarthria, dysphagia, and fatigable chewing.
Myasthenic crisis is a life-threatening condition, defined
as weakness from acquired MG that is severe enough to
necessitate intubation, or delay extubation following surgery.
Myasthenic crisis may be precipitated by a variety of factors
including infection, surgery, or tapering of
immunosuppression.
The diagnostic approach to myasthenia is focused on
confirming the clinical diagnosis by clinical history and
typical examination findings. Bedside tests (the Tensilon test
and the ice pack test) are easy to perform and are sensitive,
but they have major limitations due to concerns about excess
false-positive results with these techniques. More reliable
laboratory methods that aid in the confirmation are serologic
tests for auto-antibodies and electrophysiological studies
(repetitive nerve stimulation studies and single-fiber EMG).
Repetitive nerve stimulation (RNS) studies and single-fiber
electromyography (SFEMG) have a diagnostic sensitivity of
about 75 percent and 95 percent, respectively, in generalized
myasthenia. In RNS study, the nerve is electrically stimulated
6 to 10 times at low rates (2 or 3 Hertz). The compound muscle
action potential (CMAP) amplitude will not change in normal
population, but it will decline progressively in MG patients.
A RNS study is considered positive if the decrement is greater
than 10 percent. Single-fiber electromyography (SFEMG) is more
technically demanding than RNS and is less widely available,
but it is the most sensitive diagnostic test for MG. SFEMG is
positive in greater than 95 percent of those with generalized
myasthenia. In ocular MG, it ranges from 90 to 95 percent.
There are four basic therapies used to treat MG:
symptomatic treatments (anticholinesterase agents,
pyridostigmine bromide), chronic immunomodulating treatments
(corticosteroids and other immunosuppressive drugs), rapid
immunomodulating treatments (plasma exchange and intravenous
immune globulin), and surgical treatment (thymectomy).
Acetylcholinesterase inhibitors provide only symptomatic
therapy and are usually not sufficient in generalized
myasthenia. The administration of moderate or high doses of
corticosteroids leads to remission in about 30 percent of
patients and marked improvement in another 50 percent. The
rapid immunomodulating therapy provides quick onset and
transient benefit treatment. It is used in select situations,
including: myathenic crisis, preoperatively before thymectomy
or other surgery, bridge to slower acting immunotherapies and
periodically maintain remission in patients that is not well
controlled. Patients with thymoma clearly need surgical
treatment. However, the need for thymectomy is less certain in
those with nonthymomatous tissue. The likelihood of
medication-free remission is about twice as high with
thymectomy than without. The benefit of thymectomy is delayed
and accrues over several years postoperatively.
<References>
- Drachman, DB. Myasthenia gravis. N Engl J Med 1994;
330:1797.
- Meriggioli, MN, Sanders, DB. Myasthenia gravis:
diagnosis. Semin Neurol 2004; 24:31.
- Saperstein, DS, Barohn, RJ. Management of myasthenia
gravis. Semin Neurol 2004; 24:41.
- Vincent, A, Newsom-Davis, J. Acetylcholine receptor
antibody as a diagnostic test for myasthenia gravis: results
in 153 validated cases and 2967 diagnostic assays. J Neurol
Neurosurg Psychiatry 1985; 48:1246.
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