Ocular myasthenia gravis - IOVS
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Ocular myasthenia gravis
Kermit E. Osserman
The symptoms, clinical classification, diagnosis and differential diagnosis, and treatment of
myasthenia gravis of the extraocular muscles.
M. .yasthenia gravis is a disorder charac-
terized by fatigability and abnormally
these muscles or evidence of any central
nervous system lesion.1
rapid exhaustion, with loss of strength in Since mild myasthenia gravis often re-
muscles under voluntary control and a re- mains undetected, and occasionally ful-
turn of strength, at least in part, after a minating cases may die undiagnosed, esti-
period of rest or administration of anti- mation of the true incidence of this disease
cholinesterase drugs. is difficult. An educated guess would place
The term myasthenia gravis comes from the incidence in the United States at one
the Greek mys (muscle) plus asthenia in 20 to 30 thousand. Sex and age distribu-
(weakness), and from the Latin gravis tion of myasthenia has been remarkably
(heavy), and implies a marked or severe similar in major groups of patients ana-
muscle weakness. This weakness does not lyzed8; incidence in female to male subjects
necessarily have to be "gravis" to be is a 3:2 ratio. However, the greatest inci-
"myasthenia." Undoubtedly, because of the dence in women is in the third decade in
mild character of the symptomatology in life whereas in men it is in the sixth or
some cases, many remain undiagnosed and seventh decade. Onset may be at any age
untreated.1 from birth to the ninth decade.
Pathophysiology of myasthenia gravis
has been demonstrated at the neuromus- Symptoms
cular junction, and whether this be pre- One of the commonest signs of myas-
synaptic or postsynaptic has not been thenia gravis is unilateral or bilateral ptosis.
settled at the present time, although evi- Frequently ptosis shifts from one eye to
dence leans toward the former.- There is the other and when this is seen it is pathog-
a lack of correlation between prominent nomonic of this disease.1 Occasionally the
weakness and abnormal physiologic re- upper lid is so retracted that the eye is kept
sponses of certain involved voluntary mus- extremely wide open and patient is unable
cles and any demonstrable pathology of to close the eye completely. This phe-
nomenon is always unilateral, the other
lid being ptosed. This is seen in treated
cases. Although ptosis may be the only
From the Department of Medicine, Myasthenia evident sign of myasthenia gravis, systemic
Gravis Clinic and Research Laboratory of The
Mount Sinai Hospital, New York, N. Y.
examination may reveal unsuspected weak-
This work was supported by a grant from The
ness or fatigability in muscles other than
Tillie Lewis Foundation. those obviously involved. In most patients
277
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]une 1967
ptosis is accompanied by diplopia and Clinical classification
blurring of vision. These ocular signs and Symptomatology at onset does not neces-
symptoms, especially ptosis, are made sarily indicate eventual total involvement.
worse by bright light. In about 70 per cent Classification of the individual patient
of patients, one or another of the eye symp- should be dynamic, with initial classifica-
toms described above will mark the onset tion revised as the disease progresses. As
of myasthenia, and after a period of time a result of careful study of over 800 pa-
they will be seen in at least 90 per cent of tients, a Clinical Classification has been
all patients. Frequently after the onset of developed which takes into account not
eye symptomatology, other striated muscle only initial symptomatology, age at onset,
weaknesses will be apparent in the form and sex, but also for progress of the dis-
of myasthenic facies caused by weakness ease. In addition to its prognostic value,
of facial muscles. This is responsible for the this classification is a guide for selection of
snarl which may develop when myasthenic therapy. According to age at onset, pa-
patients are asked to smile or show their tients are divided into pediatric and adult
teeth. As a meal progresses, weakness of groups as follows.1-5
jaw muscles may cause difficulty in chew- Pediatric group. The pediatric myas-
ing and dysphagia, which frequently re- thenia gravis group includes neonatal and
sults in nasal regurgitation of fluids. Diffi- juvenile patients.
culty in speech in the form of dysarthria, Neonatal group. Neonatal myasthenia
characterized by a nasal "twang," is often gravis occurs only in infants bom of myas-
heard. When starting to speak the voice thenic mothers and is a self-limited condi-
is relatively clear and the speech is easy tion lasting no more than six weeks. It is
to understand; as speech continues, volume probably caused by transmission of an
of voice and clarity of speech decrease. etiologic factor across the placental barrier.
Respiratory distress may be seen in some Progression to juvenile myasthenia has been
cases. This may be either inspiratory or reported in only one instance.1
expiratory depending upon muscle groups Juvenile group. Unlike the neonatal form,
involved. In milder cases, respiratory dis- clinical myasthenia gravis is not present in
tress occurs only during exercise. A rela- the mothers of these children. The juvenile
tively uncommon sign of myasthenia gravis form may develop at any time from
is a longitudinal furrowing of the tongue birth to puberty, and tends to be perma-
called "myasthenic tongue." nent. In those infants in whom the disease
The skeletal muscles most frequently in- begins at birth, there may be an apparent
volved are those of neck, shoulder, and confusion with the neonatal form but the
hip girdles. Proximal leg muscles are mother's status and permanence of the
affected more often than distal ones; ex- defect soon define the actual classification.
tensors of upper extremities are involved Siblings and close relatives of juvenile
more frequently than the flexors. These myasthenia patients may also have myas-
symptomatologies are asymmetric in most thenia gravis. Ophthalmoplegia with severe
adult patients. ptosis, bilateral, partial or complete, is
Early atrophic changes of involved mus- common in this group and is often resistant
cle groups do occur and do not rule out to drug therapy. Symmetrical limb involve-
diagnosis of myasthenia gravis. Ocular ment is also frequently present. The nature
pain, headache, paresthesias,1 and other and degree of the myasthenic defect indi-
sensory changes have been noted at one cate inclusion of these patients into the
time or another in about 14 per cent of more descriptive divisions of the adult
patients.1 The pain becomes more severe groups below.
as the day progresses, but it usually re- Adult group. Adult myasthenia gravis
sponds to rest or anticholinesterase medica- patients have been divided into four
tion. groups.
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Group I. Ocular myasthenia. This is a correlated with disuse and not associated
localized form frequently limited to only with any demonstrable lesions of central
one eye and characterized by ptosis and and peripheral nervous systems. Electro-
diplopia. This group has an excellent prog- myography of involved muscle groups re-
nosis and, if there, is no spread of myas- veals a characteristic myopathic pattern.
thenic involvement to other muscle groups
within two years of onset, the disease usu- Diagnosis
ally remains nonprogressive. Of 833 myas- Diagnosis of myasthenia gravis is simple
thenic patients, 21 per cent are in this when the patient presents classical symp-
group. toms; however, diagnosis early after onset
Group HA. Mild generalized myasthenia of a mild form may be difficult, and a high
grams. This form is characterized by slow degree of awareness of myasthenia gravis
onset, frequently ocular, gradually spread- is necessary. Of utmost importance is dili-
ing to skeletal and bulbar musculature. gence in eliciting the following details
The respiratory muscles are spared. The when obtaining the patient's history: onset
response to drug therapy is good and the of weakness and its diurnal variation; effect
mortality rate is very low. of rest; influence of menstrual cycle, infec-
Group 1IB. Moderate generalized myas- tion, and emotional stress; response to medi-
thenia grams. This form has a gradual cations; tolerance of average and unusual
onset with frequent ocular presentation, physical activity; possible history of remis-
progressing to more severe generalized in- sions followed by exacerbations. Shift of
volvement of the skeletal and bulbar mus- ptosis from one eye to the other is almost
culature. Dysarthria, dysphagia, and poor pathognomonic of myasthenia gravis. The
mastication are more prevalent than in possibility of neurotic asthenia which may
Group IIA. The respiratory muscles are closely resemble myasthenia gravis can be
not involved. The response to drug therapy excluded by critical and objective assess-
is less satisfactory and the patient's activi- ment of alleged weakness.
ties are restricted, but the mortality rate The basal state (nonmedicated) is essen-
is low. tial for thorough physical and neurologic
Group III. Acute fulminating myasthenia examination. In mild cases, physical activ-
grams. This form has a rapid onset of ity may be necessary to provoke muscle
severe bulbar and skeletal muscle weakness weakness. Although routine laboratoiy tests
with early involvement of respiratory mus- usually have no diagnostic value in myas-
culature. Progression of the disease is thenia gravis, such studies as chest radiog-
usually complete within six months. The raphy (with tomography if indicated),
percentage of thymomas is highest in this thyroid evaluation, lupus erythematosus
group. The response to drugs is poor, and preparations, and immunologic testing of
the incidence of myasthenic, cholinergic, sera may be helpful. An enlarged thymus
and mixed crises is high; the mortality rate is a common finding.1
is also high. Most diagnostic doubts can be eliminated
Group IV. Late severe myasthenia gravis. through the use of pharmacologic tests,
In this form, severe myasthenia gravis reparative or provocative, with or without
develops at least two years after onset of electromyography and ergography/' Drugs
Group I or Group II symptoms. Progression in current use are edrophonium chloride
of myasthenia gravis may be either grad- (Tensilon), neostigmine (Prostigmin), d-
ual or sudden. This group has the second tubocurarine (curare), and decametho-
highest percentage of thymomas. The re- nium. Quinine is no longer advocated as a
sponse to drug therapy and the prognosis provocative test because of attendant
are poor. hazards.
Some patients in Groups II and IV may To detect false-positive responses to drug
demonstrate localized muscle atrophy, not tests, parallel tests should be performed
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June 1967
with a placebo, preferably in a double-
blind fashion.
If weakness is experienced in the pharyn-
geal constrictors, fluoroscopic examination
during swallowing of a contrast medium
before and after administration of an anti-
cholinesterase drug often has diagnostic
value.
Edrophonium chloride test. Osserman
and Kaplan0 developed the edrophonium
chloride test for my asthenia gravis which,
Fig. 1. Patient with oculobulbar myasthenia gravis.
in its present form,7 is performed as fol- Left, before injection of edrophonium chloride.
lows: the patient's muscle strength is Right, relief of ptosis and better facial expression
evaluated both subjectively and objectively, 30 seconds after injection of edrophonium chloride.
measuring the width of the palpebral fis- {Reprinted from Osserman, K. E.: Myasthenia
sure and the range of extraocular muscle Gravis, New York, 1958, Grune & Stratton, Inc.,
p. 95.)
movements. For the latter, the red-glass
or red-bar tests are helpful. Skeletal mus-
cles involved in the myasthenic process placebo. Either 20 mg. of nicotinic acid,
are tested by using the dynamometer and 200 mg. of calcium chloride, or 0.3 to 0.4
the ergograph. Vital capacity is measured mg, of atropine will be suitable for this
with a ventilation meter, and chewing and purpose. Advantages of the edrophonium
swallowing are observed. Following a 4 chloride test are: it can be repeated with-
to 6 minute rest period, 2 mg. of edropho- in 10 minutes; its action is rapid and tran-
nium chloride is injected intravenously and sient, enabling both physician and patient
muscle strength is again evaluated within to observe repeatedly the effects of anti-
30 to 90 seconds. If an inadequate response cholinesterase medication; muscarinic side-
results from this dose, increments up to 8 reactions are less frequent and less severe
mg. of edrophonium chloride should be than after neostigmine, and they disappear
tried after a 2 minute delay. If the 2 mg. rapidly.
dose gives a cholinergic response, the test Edrophonium chloride tonometry. Recent
should be repeated 30 minutes later with reports indicate that increased tension in
a dose of 0.5 to 1.0 mg. Subjective com- the eyeball of the myasthenic patient is
plaints of diplopia may remain unchanged found by tonometry when edrophonium
after edrophonium chloride testing al- chloride is administered.s>9 To date, at The
though the examiner may be able to dem- Mount Sinai Hospital, New York, we have
onstrate that the original weak muscle is not evaluated this use of edrophonium.
corrected by edrophonium, and a previ- Neostigmine methylsulfate test. With
ously uninvolved muscle is weakened by the introduction of neostigmine, adminis-
a cholinergic response. This type of reac- tration of this drug became the basic pro-
tion to edrophonium is a positive test for cedure in diagnosis.10 It may be given in
my asthenia gravis. The edrophonium chlo- one of two ways: (1) intramuscular injec-
ride test in a patient with oculobulbar tion of 1.5 mg. of neostigmine methyl-
myasthenia gravis is illustrated in Fig. 1. sulfate alone or combined with 0.6 mg. of
If one suspects that weakness is functional atropine sulfate or, (2) intravenous injec-
or the result of other muscular or central tion of 0.5 mg. of neostigmine methyl-
nervous system diseases rather than myas- sulfate. The commonest means of testing
thenia gravis, one should pair the edropho- with this drug is the intramuscular route.
nium chloride injection in a double-blind The patient is given an injection and re-
fashion with intravenous injection of a examined at 5 to 10 minute intervals for
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45 to 50 minutes, with both subjective and the evidence of abnormality of the motor
objective improvement or lack of it being unit which it reveals is or is not compatible
noted. The same observations are carried with the clinical diagnosis under considera-
out with intravenous testing; however, the tion. Electromyographic results must be in-
response starts within one to two minutes. tegrated with results of other tests, clinical
False-negative results with this test may examination, and history in arriving at a
occur because of the size of the dose: the diagnosis. However, electromyography is
patient may be sensitive to neostigmine not a necessary routine for diagnosis. Phar-
and with the dosage used the weakness macologic tests usually are reliable and are
of the disease may be replaced with the not difficult to perform in clinic or office.
weakness of overdepolarization. This test The real value of electromyography is seen
cannot be repeated with increasing dosages when other tests produce equivocal results
at the same visit; therefore, testing with a or when objective tests are needed because
different dosage must await a subsequent of difficulty in interpreting clinical data,
visit. even though compared with a placebo
Curare test. Occasionally, in a patient test.1
with mild, generalized myasthenia gravis, Bremen1'1 has developed a technique
information obtained from the edrophoni- combining electromyography without stim-
um or neostigmine test may be confusing. ulation and the edrophonium test. This
When this occurs, additional information technique requires subconjunctival inser-
may be obtained by using cZ-tubocura- tion of fine gauge, concentric electrodes
rine.11'n- Because persons with myasthenia directly into extraocular muscles with the
gravis are very sensitive to very small doses use of only topical anesthesia. This is a
of d-tubocurarine, utmost caution is neces- simple, practical procedure devoid of
sary: this test should be used only in those harmful effects; the only complication is
cases in which definite diagnoses cannot the occasional occurrence of a sub-
be obtained with edrophonium and neo- conjunctival ecchymosis, which is a cos-
stigmine tests. When performing this test, metic blemish of brief duration. Muscle
it is imperative to have at hand drugs and action potentials are suitably amplified,
equipment necessary for respiratory resus- displayed on dual-beam oscilloscopes, and
citation and also physicians thoroughly recorded with moving film photography.
competent in their use.1 Utilization of electromyography to evalu-
Decamethonium test. In myasthenia ate drug action has revealed a striking and
gravis there is resistance of clinically non- characteristic muscle response even though
involved muscles to intravenous adminis- gross improvement in motility may not be
tration of decamethonium. Because severe evident.
respiratory depression may develop during In the past decade, immunologic studies
the decamethonium test, the same safe- have shown that an antibody may be found
guards necessary for the curare test should in the sera of 40 per cent of myasthenic
be provided. In normal subjects, decame- patients. Weiner and Osserman15 have
thonium produces marked reduction in found this antibody in 32 per cent of Group
height of action potential and considerable I ocular myasthenia patients studied. Al-
muscle weakness. Subsequent injection of though this test at present cannot be used
anticholinesterase (e.g., edrophonium) in- as a completely diagnostic procedure, it
creases generalized weakness. In myasthe- lends support to clinical and phannacologic
nic subjects, relatively large doses of dec- observations.
amethonium cause little or no reduction
in height of action potential or strength of Differential diagnosis
noninvolved muscles.13 Isolated ocular symptoms, either ptosis
Electromyography aids in diagnosis when or diplopia, occur in many neurologic dis-
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June 1967
orders. Characteristic of strabismus seen eurysiri; A bruit heard over the eye is char-
as a congenital or heredodegenerative pro- acteristic of aneurysm. If there is dimin-
cess is the static, nonprogressive nature of ished comeal sensation in the involved eye,
the ocular sign from birth on. But even this this diagnosis becomes a probability and
need not be an absolute differentiation. A myasthenia gravis is excluded. In cranial
patient has been seen who had congenital neuropathies associated with diabetes,
strabismus of the external type superim- syphilis, diphtheria, and the so-called
posed upon which myasthenia developed; Guillian-Barre syndrome, the total clinical
its effects were limited to an increase in picture is essential for differentiation of
the degree of external rotation of the left these conditions from myasthenia gravis. If
eyeball and demonstrable only by the re- myasthenia is still suspected, response of
sponse of the eyeball to anticholinesterase symptoms to anticholinesterase medication
medication. Congenital ptosis of the lids again becomes the diagnostic feature. In
is perhaps most often confused with my- multiple sclerosis, ocular symptoms are
asthenia gravis, but this, too, is a disturb- most often accompanied by nystagmus, and
ance exhibited at birth and nonprogressive true nystagmus is rarely seen in myasthenia
in nature. In these cases familial history, gravis. Nystagmus caused by multiple scle-
the static nature of the ptosis, the history rosis results most often from involvement
of its presence since birth, as well as nega- of the median longitudinal bundle, with
tive responses to anticholinesterase medica- resultant horizontal and vertical nystagmus
tion serve to differentiate the condition diagnostic of involvement of the brain-
from myasthenia gravis. stem. Temporal pallor of the optic disks is
Involvement of oculomotor, trochlear, commonly seen in multiple sclerosis. Of
or abducens nerves by any number of course, if there is evidence of central ner-
processes, including infections, trauma, vous system involvement, the diagnosis is
and neoplasm, produces characteristic ocu- multiple sclerosis.
lar palsies which do not have the fluctuat- Unilateral ptosis as an isolated sign or
ing characteristics of myasthenia gravis. symptom may be congenital, or due to in-
Myasthenic involvement of external ocular volvement of the ocular sympathetic nerves
muscles may closely simulate any of the or the oculomotor nerve, or it may be my-
ocular palsies. It has been said that, when asthenic in origin. Congenital ptosis, as
myasthenia gravis discretely involves one previously described, exists from birth and
eye in a manner which produces what ap- does not vaiy. Involvement of ocular sym-
pears to be a typical third nerve palsy, a pathetic nerves produces a Homer's syn-
differential point of significance is absence drome, in which case ptosis is accompanied
of involvement of the pupil. Since periph- by ipsilateral miosis, enophthalmos, and
eral involvement of the oculomotor nerve diminished sweating over the same side of
is almost invariably accompanied by an the head and face. Ptosis produced by third
internal as well as external ophthalmople- nerve palsies is accompanied by dilatation
gia, this is used as a distinguishing char- of the pupil as well as specific ocular pal-
acteristic. There are reports in the litera- sies related to involvement of the third
ture of isolated cases of myasthenia gravis nerve. In these cases, the eye is commonly
involving the ciliary muscle. In such rare deviated externally because of unopposed
instances, ultimate differentiation may de- pull of the external rectus muscle. Diag-
pend upon response to anticholinesterase nosis of myasthenia gravis is confirmed by
medication. the response of the ptosis to anticholin-
When diplopia and/or ptosis are ac- esterase medication.
companied by localized headache over the Weakness exclusively in the limbs may
involved eye or by pain in the eye, one resemble that present in muscular dystro-
must think seriously of an intracranial an- phy, motor neuropathies, or amyotonia con-
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genita. Symptoms of chronic fatigue may gastric distress including nausea, abdom-
mimic those of myasthenia gravis, but re- inal cramps, diarrhea, and fasciculations)
sponse to specific testing is different. En- which are pronounced and sometimes diffi-
docrine disorders and the "Eaton-Lambert- cult to control even with atropine sulfate.
Rooke syndrome" also may simulate myas- Because atropine sulfate obscures early
thenia gravis. No therapeutic test is abso- signs of incipient overdosage it should not
lutely pathognomonic. Hysteria can simu- be used routinely. Neostigmine bromide is
late almost any symptomatology known. available as a 15 mg. scored tablet and
False-positive or false-negative edrophoni- usually is prescribed for use eveiy two to
um or curare tests can result in errors in three hours. Dosage is variable, not only
diagnosis. Proper testing with placebos in between patients but also for the same pa-
the former usually precludes this error. tient on the basis of stress from physical
However, Schwab and Perlo10 reported a activity, menses, infection, or emotional
group of patients having a variety of neu- trauma. While no specific dose can be
rologic syndromes who had definite false- recommended, it usually is safe to start a
positive reactions to edrophonium and neo- new patient on one tablet three times a
stigmine testing. Rare false-negative re- day.
sults occur when either negligible objective Pyridostigmine (Mestinon) bromide. This
response is noted or overdosage with the drug is an analogue of neostigmine and
test drug causes a cholinergic reaction. To more effective in relieving myasthenia
rule out false-negative responses, any syn- symptoms in small .muscles innervated by
drome of muscle weakness, not accom- cranial nerves, particularly those involved
panied by alteration of tendon reflexes, in in ptosis, diplopia, and dysarthria. Its di-
which there is some improvement of urnal duration of action is approximately
strength after administration of correct half an hour longer than that of neostig-
amounts of neostigmine or edrophonium mine. However, one of the chief advan-
should be considered to be myasthenia tages of pyridostigmine is its longer noc-
gravis. A history of remissions in the past turnal action, obviating administration dur-
or evidence of thymic abnormality tends ing the night and enabling even the pa-
to confirm the diagnosis. A positive edro- tient with dysphagia to swallow the first
phonium or neostigmine test serves to con- dose in the morning. Another salient ad-
firm the clinical impression derived from vantage of pyridostigmine over neostig-
history and physical examination. When mine is its smoother action, low incidence
tests are properly performed with placebos of muscarinic side-effects, and resultant
and mechanical and electrical measure- marked decrease in need for routine use
ments are used, the diagnosis rarely re- of atropine sulfate. Although the range of
mains in doubt. therapeutic and toxic levels of pyridostig-
mine is much greater than that of neostig-
Treatment mine, the usual side-reactions do occur with
Pharmacologic therapy depends upon a overdosage. Most patients using pyridostig-
group of relatively short-acting potent anti- mine are satisfied with the sustained feel-
cholinesterases. ing of well-being throughout the day.
Choice of drugs. Pyridostigmine bromide is available as a
Neostigmine bromide. This drug has ^-scored 60 mg. tablet, usually replace-
been used effectively for three decades. It able tablet-for-tablet with neostigmine, and
is not habit forming; the requirement de- prescribed every three to four hours in
creases if myasthenia remits. Its two dis- most cases. Prolonged-action pyridostig-
advantages are short duration of action mine bromide is available as a scored
(approximately two hours) and side-effects "Timespan" tablet containing 180 mg.,
(sweating, salivation, lacrimation, and epi- which has the immediate effect of a reg-
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June 1967
ular 60 ing. tablet. Its slow release of pyri- termined. They may be used in combina-
dostigmine produces a duration of action tion with oral neostigmine or pyridostig-
approximately 2 to 2V2 times that of a reg- mine, but never with ambenonium, as there
ular pyridostigmine tablet. Its primary ad- is a marked synergism with the latter,
vantage is its production of extended noc- which may cause cholinergic crisis.1 s
turnal relief; frequently it is prescribed for Combinations. When a single drug will
the last dose of the day, regardless of which not effect adequate control, some patients
drug may be used throughout the day. may be treated more satisfactorily with
Ambenonium (Mytelase) chloride. This combinations of anticholinesterase drugs.
drug is a bis molecule and is wholly differ- Pyridostigmine and ambenonium are more
ent in structure from neostigmine or pyri- effective in predominately bulbar involve-
dostigmine. Its effect on involved pe- ment, whereas neostigmine and ambeno-
ripheral muscles is excellent and results in nium are better for control of peripheral
more sustained increase in strength. For muscular weakness. Combined drug ther-
bulbar myasthenia ambenonium is mid- apy should be reserved for patients with
way between pyridostigmine and neostig- relatively stable myasthenia and of proved
mine in value. While its action is definitely intelligence in handling their own drug
longer than that of neostigmine, and per- dosages.
haps slightly longer than that of pyrido- Adjuvant drugs. In isolated cases, use of
stigmine for diurnal use, its nocturnal ef- ephedrine sulfate and potassium salts still
fect is the same as that of regular pyrido- meets with some favor and results in occa-
stigmine. It has fewer toxic side-effects sional improvement. Ephedrine sulfate, 25
than neostigmine, but more than pyrido- mg. three times a day, gives an increase in
stigmine, and they differ in nature. More strength to some patients not fully con-
prominent are central nervous system side- trolled with anticholinesterase therapy
effects such as headache. Other early signs alone. Potassium salts in liquid form, 15
of overdosage are fasciculations and mus- mEq. three times a day, may also be help-
cular weakness. Gastrointestinal side-reac- ful. Instead of potassium salts, intracellular
tions are less common, but they do appear potassium-sparing drugs such as spirono-
later when overdosage is imminent. For the lactone (Aldactone-A), 25 mg. four times
patient on a respirator, ambenonium has a day, or triamterene (Dyrenium), 100
the distinct advantage of causing less bron- mg. twice a day, may be employed. Thus,
chial secretions than do other anticholin- ephedrine sulfate and any one of the three
esterase drugs. Ambenonium chloride is adjuvants affecting potassium may be used
available as scored tablets of 10 and 25 mg. separately or together in addition to the
Approximately 6 mg. of ambenonium chlo- basic treatment of anticholinesterase medi-
ride is equivalent to 15 mg. of neostigmine cations. If no improvement is evident, ad-
bromide or 60 mg. of pyridostigmine bro- juvant drug therapy should be discon-
mide. Ambenonium should be started cau- tinued.
tiously with a 5 mg. dose and gradually Thymectomy and radiotherapy are not
increased to therapeutic levels. indicated in the treatment of ocular myas-
Instillations of strong, long-lasting anti- thenia, and the use of adrencorticotropic
cholinesterases such as echothiophate io- hormone (ACTH) has not proved to be of
dide (Phospholine iodide) have been ad- value in this form of the disease.19
vocated for treatment of ptosis and extra-
ocular muscle weakness. When effective, Edrophonium test in management
these drugs usually relieve ptosis better In drug management of the myasthenic
than diplopia.17 These long-lasting anti- patient7' -° there are three ways to deter-
cholinesterases should not be administered mine optimal dosage for the selected drug:
unless red-cell esterase activity can be de- (1) use of empiric dosage by means of
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clinical judgment; (2) use of the edro- ages according to a table of equivalents
phonium chloride test, and (3) use of in- (Table I).
travenous titration with pyridostigmine After the patient has been started on an
bromide or neostigmine methylsulfate. Ex- anticholinesterase drug by either of the
treme caution is required because of the above methods, dosage regulation can be
serious hazard involved in the intravenous accomplished by performing an edrophoni-
titration. um test one hour after the patient has
When the diagnosis of myasthenia gravis taken his treatment drug. Three possible
is established, treatment with one of the responses are presented in Table II.
anticholinestera.se drugs is started. One If improvement of muscle strength follows
may empirically prescribe a tablet for use administration of edrophonium, the oral
at specific intervals, usually three times a dosage may be increased by one quarter
day, and observe duration of action, im- to one half of a tablet. If the patient be-
provement in striated muscle strength, and comes worse, the oral dosage should be
occurrence of side-effects. The dosage is decreased by one fourth to one half of a
gradually increased until the patient ob- tablet. If the patient shows no change in
tains maximal improvement with minimal strength, the dosage is adequate and should
side-reactions. not be adjusted at that time. If the response
For intravenous titration one gives small is adequate but the patient is still poorly
increments of pyridostigmine or neostig- controlled, use of adjuvant drugs or possi-
mine at 2 minute intervals until maximal ble reassessment of therapy should be con-
improvement is obtained. This intravenous sidered.
dose can then be translated into oral dos- In management, there are variations in
amounts of edrophonium chloride used.
One must differentiate between dosages
recomended for diagnostic testing and
Table I. Table of equivalents dosages required for regulation and con-
Intra-
trol of treatment medications.7 Our recom-
venous Oral mended test dosage for regulation of the
dose dose required amount of anticholinesterase drug,
Drug (mg.) (mg.) based on thousands of tests, is 0.2 ml. (0.2
Pyridostigmine bromide mg.) of edrophonium chloride administered
(Mestinon) 2.0 60 intravenously one hour after intake of the
Pyridostigmine bromide
(Timespan) 2.0 180 oral treatment drug. With this small dose,
Neostigmine methylsulfate edrophonium per se causes little interference
(Prostigmin) 0.5 — in reaction; effects observed clearly deline-
Neostigmine bromide — 15
Ambenonium (Mytelase) ate a response based on the oral drug admin-
chloride — 6 istered one hour earlier. Other investi-
Table II. Responses to edrophonium test
Myasthenic Adequate \ Cholinergic
Muscle strength (ptosis, diplopia, dysphonia, dysphagia, Improvement No change Worse
dysarthria, respiration, limb strength)
Fasciculations (orbicularis oculi, facial muscles, limb Absent Present or Present or
muscles) absent absent
Side-reactions (pallor, lacrimation, diaphoresis, salivation, Absent Minimal Severe
abdominal cramps, nausea, vomiting, diarrhea,
headache)
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June 1967
gators have recommended doses of 3, 4, edrophonium testing and (2) those whose
and even 10 mg. At times, with these high- ptosis responds better than does the extra-
er doses, certain areas of muscle weakness ocular muscle weakness, thereby giving
are improved while other striated muscles prominence to the more disabling aspect
become weaker. Thus, the test is difficult of their problem. In these patients, resort
to interpret. However, such a dichotomy to mechanical aids is helpful. Dark glasses
will occasionally result even with the use may help to relieve ptosis; a plastic or wire
of 0.2 ml. (2.0 mg.). In such instances, it lid crutch attached to the eyeglass frame
is the safer course to consider the current may be worn to correct the ptosis. It may
drug dose to be adequate rather than risk be advisable to use an eye patch or opaque
possible cholinergic weakness by increasing corneal lens to obscure the vision of one
the oral dosage. Only rarely does increas- eye and thus relieve the diplopia. Prism
ing the dose of edrophonium chloride to 4 lenses may be prescribed to correct mild
or 5 mg. give additional information. degrees of extraocular muscle weakness;
In some myasthenia gravis patients it is however, the degree of prism needed varies
important to compare the results of the with the patient's myasthenic condition,
edrophonium test with those of a placebo which often varies with time of day and
injection. The physician must be acutely activity. Thus, prisms are rarely successful
aware of the fact that the myasthenic pa- in relieving diplopia.
tient quickly learns to differentiate the Various operations have been performed
effects of edrophonium and placebo. to correct ptosis and diplopia. In myasthe-
The edrophonium test can be used to nia gravis, surgery is not justified, because
determine the frequency as well as the the patient's condition changes with time.
quantity requirement of anticholinesterase Unless edrophonium testing and ocular
medication, although this use is not im- electromyography indicate that the muscle
portant in the patient who is easily con- involved shows little evidence of response
trolled. Where regulation is difficult, espe- to neuromuscular treatment drugs, surgical
cially in the seriously ill myasthenic pa- procedures may prove to be a handicap.
tient, edrophonium testing should be per-
formed at the end of a dose period to avoid REFERENCES
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