Neuro4Nurses
Myasthenia Gravis
Myasthenia Gravis (MG) is an autoimmune
disease that affects the acetylcholine receptors
(AChRs) at the post-synaptic region of the
neuromuscular junctions (NMJ). Patients with MG
are presented with weakness and fatigue. The
weakness increases during repeated use and may
improve following rest or sleep1.
Epidemiology
Myasthenia gravis affects individual of all ages
with an annual incidence of 0.25 to 2 cases per
100,000 people. MG has a higher incidence in
women than men with 3:2 ratios. Peak incidents for
women are in their twenties and thirties and men are
in their fifties and sixties1.
Pathophysiology
Skeletal muscle movement is determined by the
release
and
uptake
of
neurotransmitters
[acetylcholine (ACh)] between the presynaptic
neurons and the postsynaptic receptors2.
In MG, the anti-AChR antibodies reduce the
number of the functional AChRs, widened the
synaptic cleft, and damage the postsynaptic muscle
membrane1.
About 20% of MG patients with generalized MG
do not have anti-AChR antibodies (seronegative
MG). Instead some of these patients carry the
muscle anti-specific kinase (MuSK) antibodies.
Damage to the MuSK leads to a reduced number of
AChRs and changes in AChR clustering3. Other
seronegative MG patients (~5%) who do not have
anti-AChR antibodies or anti-MuSK antibodies may
have plasma factor that inactivates the AChRs4.
Signs and Symptoms
In about 65% of patients with MG, the initial
symptoms or signs are diplopia, ptosis, extraocular
muscle weakness, or ocular misalignment5. Ptosis
can be unilateral or bilateral. Pupillary response to
light and accommodation are normal2. If weakness
remains restricted to the extraocular muscle, these
patients are said to have ocular myasthenia gravis1.
Approximately half of the patients who present
with ocular myasthenia gravis, the symptoms
progress to the other bulbar muscles and limb
muscles, resulting in generalized MG (GMG) within 2
years4,5,6. Patient may present with a snarling
expression when smiling, nasal timbre speech,
dysphagia, and dysarthria. The muscle weakness in
MG is painless and occurs after repetitive movement
or use. The limb weakness in MG is often proximal
and may be asymmetric. Deep tendon reflexes and
sensory function are preserved1,4,7.
Diagnostic Tests
Besides clinical history, diagnosis tests of MG
include neurophysiological examinations (repetitive
nerve stimulation or single-fiber electromyography),
assay for anti-acetylcholine-receptor antibody, and
administration of short acting acetylcholine esterase
inhibitors (Edorphonium)8.
Computer tomography (CT scan) and magnetic
resonance imaging (MRI) have been used to
evaluate changes of the thymus gland in MG
patients.
Edrophonium (tensilon) has a rapid onset (30 sec)
and short duration (5 min). A positive result means
after administration of edrophonium, the patient has
improvment in weakness of extraocular muscles,
impairment of speech, or the length of time that the
patient can maintain the arms in forward abduction1.
Ice pack test is putting an ice pack on the closed
eye with ptosis. After a minute or two, patient will
improve for positive result because cooling improves
neuromuscular transmission and reduce the ptosis9.
Treatment Options
There is no cure for MG, the treatment goals of
therapy are to minimize symptoms, achieve disease
remission, and maintain normal function10.
Anticholinesterase drugs are the first line of
treatment for MG. They reduce the breakdown of
acretylcholine
by inhibiting
the action of
cholinesterase and then improving muscle strength.
Pyridostigmine (MestinonTM) is the most commonly
used anticholinesterase. Its effect after oral
administration is 15 to 30 minutes, peak at 2 hours,
and last 3 to 4 hours. Common side effects of
anticholinesterase drug include abdominal cramp,
diarrhea, and increase salivation11.
Pathologic alterations of the thymus gland are
found in 75% - 85% of MG patients. Approximately
10% of this group of patients has a thymic tumor or
thymoma1,9,14. Total or extended thymectomy is the
gold standard for thymomas associated with MG16.
Robert et al (2001) stated that thymectomy
performed on patients without thymomas significantly
reduced the signs and symptoms for both ocular MG
and GMG patients14.
Oral corticosteroid therapy is usually used to treat
mild to moderate MG. Early use of steroids in MG
treatment may also decrease the risk of progression
from ocular MG to generalized MG5.
Immunosuppressants are used when MG
symptoms are not controlled with steroid therapy or
with patients who cannot tolerate the side effects of
other therapies. The most commonly used
immunosuppresants
used
for
MG
include
mycophenolate mofetil, azathioprine, cyclosporine,
cyclophosphamide, and tacrolimus. Effects of the
immunosuppressants are inhibiting of T-cell
development and function 12.
Plasmaphoresis and Intravenous immunoglobulin
(IVIG) can be used as a short term therapy for
patients whop develop a myasthenic crisis or as an
adjunctive therapy in symptomatic patients.
Myasthenic crisis
Myasthenic crisis is defined as respiratory failure
requiring mechanical ventilation1. It is related to
inadequate dosage of anticholinesterase medication
or
exacerbation
of
myasthenic
symptoms
precipitated by surgery, trauma, fever, infection, or
emotional stress 15.
Manifestations of myasthenic crisis include acute
respiratory distress, decreased urine output,
increased pulse, diminished swallowing, difficulty
speaking, double vision, and ptosis 16. Confirmation
of myasthenic crisis is a positive Edrophonium Test.
Treatment options include administration of
anticholinestearse medication, plasmaphoresis, IVIG,
and ventilation support and other supportive
interventions.
Cholinergic crisis
Cholinergic crisis is resulted from overdosage of
anticholinesterase drugs, which produce excessive
cholinergic effects. Patients present with abdominal
cramps, diarrhea, lacrimation, meiosis, excessive
pulmonary secretion, bronchospasm, fasciculations,
and weakness or paralysis of voluntary muscles 16.
Patients with cholinergic crisis will have a
negative edrophonium test. Treatments for patient
with cholinergic crisis include ventilation support and
holding anticholinesterase medications 16.
Nursing Implications
It
is
important
to
administer
the
anticholinestertase drugs on time (30 minutes
before meals) to facilitate chewing and swallowing.
Food must be eaten very slowly to prevent
aspiration. Monitor patient’s nutritional intake and
maintain a well balanced diet. Provide a modified diet
(soft or minced) when the patient developed difficulty
in eating and swallowing2,5.
The respiratory status of patients with myasthenic
crisis or cholinergic crisis can deteriorate rapidly.
Close monitoring of patient’s respiratory status such
as vital capacity, respiratory rate and pattern, SpO2,
and use of respiratory accessory muscle is crucial.
Support patient’s head and neck in a neutral
position when they developed muscle weakness.
Assist patient with the activities of daily living 2.
Suctioning equipment should be available at the
bedside to avoid aspiration.
Encourage adequate rest and avoid fatigue,
overexertion, extreme temperature, and stress2.
Reference
1) Drachman, D.B. (2008). Myasthenia Gravis and other diseases of the
neuromuscular junction. In A.S. Fauci, D.L. Kasper, D.L. Longo, E.
Braunwald, S.L. Hauser, J.L. Jameson, & J. Loscalzo. (Eds.).
Harrison’s principle of internal medicine. (17th ed.). New York:
McGraw-Hill.
2) Hickey, J.V. (2009). The clinical practice of neurological and
neurosurgical nursing. (6th ed.). Philadelphia: Lippincott Williams &
Wilkins.
3) Vinvent, A., & Leite, M.I. (2005). Neuromuscular junction
autoimmune disease: Muscle specific kinase antibodies and
treatment for myasthenia gravis. Current Opinion in Neurology, 18,
519-525.
4) Conti-Fine, B.M., Milani, M., & Kaminski, H.J. (2006). Myasthenia
gravis: Pat, present, and future. The Journal of Clinical Investigation,
116(11), 28432854.
5) Kupersmith, M.J., Latkany, R., & Homel, P. (2003). Development of
generalized disease at 2 years in patients with ocular myasthenia
gravis. Archives of Neurology, 60, 243-248.
6) Gilbert, M.E., De Sousa, E.A., & Savino, P.J. (2007). Ocular
myasthenia gravis treatment: The case against prednisone therapy
and thymectomy. Archives of Neurology, 64(12), 1790-1792.
7) Nations, S.P., Wolfe, G.I., Amato, A.A., Jackson, C.E., Bryan, W.W.,
& Barohn, R.J. (1999). Distal myasthenia gravis. Neurology, 52, 632634.
8) Schwendimann, R.N., Burton, E., & Minagar, A. (2005). Management
of myasthenia gravis. American Journal of Therapeutics, 12, 262268.
9) Czaplinski, A., Steck, A.J., & Fuhr, P. (2003). Ice pack test for
myasthenia gravis: A simple, noninvasive, and safe diagnostic
method. Journal of Neurology, 250, 883-884.
10) Antonio-Santos, A.A., & Eggenberger, E.R. (2008). Medical
treatment options for ocular myasthenia gravis. Current Opinion in
Ophthalmology, 19, 468-478.
11) Armstrong, S.M., & Schumann, L. (2004). Myasthenia gravis:
diagnosis and treatment. Journal of the American Academy of Nurse
Practitioners, 15(2), 72-78.
12) Vincent, A. (2008). Autoimmune disordwers of the neuromuscular
junction. Neurology India, 56(3), 305-313.
13) Sakamaki, Y, Kido, T., & Yasukawa, M. (2008). Alternative choice of
total and partial thymectomy in video-assisted resection of noninvasive thymomas. Surgical Endoscopy, 22, 1272-1277.
14) Roberts, P.F., Venuta, F., Rendina, E., De Giacomo, T., Coloni, G.F.,
Follette, D.M., Richman, D.P., & Benfield, J.R. (2001). Thymectomy
in the treatment of ocular myasthenia gravis. The Journal of Thoracic
and Cardiovacular Surgery, 122(3), 562-568.
15) Gunduz, A., Turedi, S., Kalkan, A., & Nuhoglu, I. (2006). Levofloxacin
induced myasthenia crisis. Emergency Medicine Journal, 23(8), 662.
16) Perlo, V.P. (2004). Treatment of the critically ill patient with
myasthenia. In A.H. Ropper, D.R. Gress, M.N. Diringer, D.M. Green,
& S.A. Mayer. (Eds.) Neurological and neurosurgical intensive care.
(4th ed.). Philadelphia: Lippincott Williams & Wilkins.
©2013
Disclaimer: The author of this article neither represent nor guarantee that the
practices described herein, if followed, ensure safe and effective patient care. The
author further assumes no responsibility or liability in connection with any
information or recommendations contained in this article. The recommendations and
instructions in this article are based on the knowledge and practice in neuroscience
as of the date of publication. These recommendation and instructions are subject to
change based on the availability of new scientific information.