TABLE 1

Key features distinguishing myasthenia gravis from other common diagnoses

DisorderSimilarities to myasthenia gravisDifferences from myasthenia gravis
Lambert-Eaton myasthenic syndromeWeakness and fatigueLess prominent ocular or oculobulbar features
Areflexia or hyporeflexia
Autonomic features (dry mouth, erectile dysfunction)
Positive antibody against P/Q voltage-gated calcium channel
High-frequencey repetitive nerve stimulation testing shows an incremental response (ie, a progressive increase in motor amplitude)
BotulismOcular findings (diplopia and ptosis), bulbar dysfunction, generalized weaknessAcute attack, possible history of food poisoning
Descending paralysis
Dilation of the pupil (mydriasis)
Prominent autonomic dysfunction
Monophasic course
High-frequency repetitive nerve stimulation testing shows an incremental response
Amyotrophic lateral sclerosisBulbar dysfunction and weaknessSlow progressive course
No ocular findings
Symptoms do not fluctuate
Findings of upper motor neuron dysfunction (eg, hyperreflexia, spasticity)
Electromyography showing prominent active and chronic denervation or reinnervation, or both
MyopathyProximal limb weaknessRelative absence of ocular findings
Symptoms do not fluctuate
Creatine kinase elevation and presence of myositis-specific antibodies in cases of autoimmune or inflammatory myositis
Repetitive nerve stimulation testing is normal, while needle electromyography shows short-duration, low-amplitude, polyphasic motor-unit potentials, with or without abnormal spontaneous activity
Guillain-Barré syndrome and chronic inflammatory demyelinating polyradiculoneuropathyGeneralized weaknessSensory symptoms such as pain and paresthesia
Symptoms do not fluctuate
Hyporeflexia or areflexia
Cerebrospinal fluid has protein elevation, no significant pleocytosis
Nerve conduction studies reveal findings consistent with demyelination
Thyroid eye diseaseDiplopiaPtosis is infrequent
Symptoms do not fluctuate
Other ocular findings such as edema, redness, conjunctival injection and exophthalmos
Magnetic resonance imaging showing extraocular tissue enlargement
Oculopharyngeal muscular dystrophyPtosis, diplopia, dysphagiaSlowly progressive course
Absence of symptomatic fluctuation
Relative absence of prominent limb weakness
Elevation of creatine kinase
Mutations in the PABPN1 gene; mostly autosomal dominant pattern of inheritance