Key features distinguishing myasthenia gravis from other common diagnoses
Disorder | Similarities to myasthenia gravis | Differences from myasthenia gravis |
---|---|---|
Lambert-Eaton myasthenic syndrome | Weakness and fatigue | Less 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) |
Botulism | Ocular findings (diplopia and ptosis), bulbar dysfunction, generalized weakness | Acute 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 sclerosis | Bulbar dysfunction and weakness | Slow 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 |
Myopathy | Proximal limb weakness | Relative 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 polyradiculoneuropathy | Generalized weakness | Sensory 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 disease | Diplopia | Ptosis 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 dystrophy | Ptosis, diplopia, dysphagia | Slowly 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 |