Myasthenia gravis
Miastenia gravis
CategoryDefinition
A disorder of neuromuscular transmission characterized by fatigable weakness of cranial and skeletal muscles. Autoantibodies directed against acetylcholine receptors damage the motor endplate portion of the neuromuscular junction, impairing the transmission of impulses to skeletal muscles. Clinical manifestations may include fluctuating diplopia and ptosis, and fatigable weakness of facial, bulbar, respiratory, and proximal limb muscles.
Diagnostic Criteria
Signs & symptoms: Manifests as painless fatigable muscle weakness. The pattern of muscle involvement varies, but extraocular muscles are most commonly affected, causing diplopia and ptosis. Limb weakness can affect any muscle group, although proximal muscles are most often affected. Symptoms typically worsen towards the end of the day and with exercise. Extreme heat, emotional stress, infection, pregnancy and menstruation can all exacerbate myasthenia, as can many drugs, including aminoglycoside antibiotics and penicillamine.