TINJAUAN PUSTAKA
CDK 172/vol.36 no.6/September - Oktober 2009
416
Diagnosis
Myasthenia gravis diagnosed from clinical characteristics. An array
of biological, pharmacological, and instruments test can assist
diagnosis. A negative result does not definitely exclude MG
(8)
.
Table 1. Myasthenia gravis classification (Osserman and Gerkins)
Differential diagnosis
Disorders of neuromuscular junction [NMJ] are clinically hetero-
geneous. The clinical expressions of these disorders are myasthenic
features in the form of variable muscle weakness and fatigability.
The name myasthenic syndromes [MS] is given to a group of
disorder of NMT with different pathophysiology from acquired
autoimmune myasthenia gravis
(9,10)
.
· Lambert-Eaton myasthenic syndrome (LEMS)
Lambert-Eaton myasthenic syndrome (LEMS) is a rare condition
caused by abnormality of acetylcholine (ACh) release at the neuro-
muscular junction. Cancer is eventually found in 40% of patients
with LEMS; usually small cell lung cancer (SCLC), although LEMS
also has been associated with other cancers(11). A comparative study
of clinical pattern between MG and LEMS from 101 patients
showed that LEMS do not affect ocular weakness in all cases
(12)
.
· Botulism
The effects of the toxin are limited to blockade of peripheral
cholinergic nerve terminals, including those at neuromuscular
junctions, postganglionic parasympathetic nerve endings, and
peripheral ganglia. This blockade produces a characteristic bilateral
descending paralysis of the muscles innervated by cranial, spinal,
and cholinergic autonomic nerves but no impairment of adrenergic
or sensory nerves. Botulism has severe, progressive, and symmetric
pattern
(13)
.
Treatment
The aim of MG treatment is to achieve three essential objectives :
(1) Optimise neuromuscular transmission, (2) Reduce or neutralise
the consequences of the autoimmune reaction, and (3) modify
the natural history of MG by inducing remission, defined as per-
manent condition of absence of symptoms without treatment(8).
AChE inhibitors and immunomodulating therapies are the
mainstays of treatment. In the mild form of the disease, AChE
inhibitors are initially used. Most patients with generalized MG
require additional immunomodulating therapy
(2)
.
Other novel treatments for MG are Plasma Exchange, Immuno-
globulin, and thymectomy. Plasmapheresis or plasma exchange
is effective, especially in preparation for surgery or as short-term
management of an exacerbation.
A consensus meeting on IVIg concluded that IVIg treatment (2g/
kgBW) was most useful in acute deteriorating disease, minimising
the risk of bulbar or respiratory weakness requiring intensive care
support. It was also useful temporarily in patients with severe
condition when other treatments had not yet effective. Use in chronic
condition and as a primary treatment was not recommended.
No significant difference was found in an randomised controlled
trial comparing plasmapheresis and IVIg treatment. Mechanism
of Immunoglobulin Therapy are: (1) Microbial and toxin inhibition,
(2) Complement deactivation, (3) Receptor Blockade, (4) Anti
Idiotypes, and (5) Modulating Cytokine Production
(14)
.
Thymectomy is an important treatment option in MG, especially
if a thymoma is present. It has been proposed as a first-line
therapy in most patients with generalized myasthenia. Thymec-
tomy may induce remission. American Association of Neurology
recommended thymectomy for nonthymomatous autoimmune
MG patients. Thymectomy is recommended as an option to
increase the probability of remission or improvement
(15)
.
Prognosis
In ocular MG, >50% of cases evolve to generalised MG within a
year, spontaneous remission in < 10%(8). Approximately 15-17%
of patients will remain having strictly ocular symptoms over a
mean follow-up period of 17 years. Those patients are referred
as ocular MG. The rest develop a generalized weakness and are
referred as generalized MG
(6).
A study of 37 patients MG showed
that the presence of thymoma associated with poorer outcome.
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343-346
Degree
Symptoms and signs
I
Purely ocular (ptosis and diplopia)
II A
Mild generalized (ocular and extremities, no prominent
bulbar
sugns)
II B
Moderate generalized (ocular and/ or bulbar signs, variable
limb muscle involvement, no crises
III
Acute fulminating generalized signs with prominent
bulbar involvement and crises
IV
Late severe generalized and prominent bulbar signs
and
crises