Neuromuscular
transmission disorder
characterized by fluctuating
weakness and fatigability of
bulbar and other voluntary
muscles without loss of reflexes
or impairment of sensation or
other neurologic function.
Diagnostic
criteria:
A.
Characteristic signs and
symptoms
One or more
of the following:
-
Diplopia,
ptosis, dysarthria, weakness in
chewing, difficulty in
swallowing, muscle weakness with
preserved deep tendon reflexes,
and, less commonly, weakness of
neck extension and flexion, and
weakness of trunk muscles
-
Increased
weakness during exercise and
repetitive use with at least
partially restored strength
after periods of rest
-
Dramatic
improvement in strength
following administration of
anticholinesterase drug (edrophonium
(Tensilón®)
and neostigmine);
and one or
more of the following:
B. EMG and
repetitive stimulation of a
peripheral nerve: In myasthenia
gravis repetitive stimulation at
a rate of 2 per second shows
characteristic decremental
response which is reversed by
edrophonium or neostigmine.
Single fiber studies show
increased jitter.
C. Antibodies
to Acetylcholine Receptors
Exclusions:
-
Congenital
myasthenic syndrome, progressive
restricted myopathies, steroid
and inflammatory myopathies,
motor neuron disease
-
Multiple
sclerosis, variants of
Guillain-Barré syndrome (e.g.,
Miller-Fisher syndrome)
-
Organophosphate toxicity,
botulism, black widow spider
venom
-
Eaton-Lambert
syndrome
-
Stroke
-
Medications:
neuromuscular blocking agents,
aminoglycosides, penicillamine,
antimalarial drugs, colistin,
streptomycin, polymyxin B,
tetracycline
-
Hypokalemia;
hypophosphatemia
Severity: (Osserman
classification):
I: Ocular myasthenia
IIA: Mild generalized myasthenia
with slow progression: no
crises, responsive to drugs
IIB. : Moderately severe
generalized myasthenia : severe
skeletal and bulbar involvement
but no crises; drug response
less than satisfactory
III: Acute fulminating
myasthenia, rapid progression of
severe symptoms, with
respiratory crises and poor drug
response
IV: Late severe myasthenia, same
as III but progression over 2
years from class I to II
Related Criteria
McDonald Diagnostic Criteria for Multiple Sclerosis (MS)
NIH Diagnostic Criteria for Neurofibromatosis
Diagnostic Criteria for Tuberous Sclerosis Complex (TSC)
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Diagnostic
Criteria and Associated Features of
Restless Legs Syndrome (RLS)
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