Neuromuscular junction disorders (Myasthenia Gravis and Myasthenic Syndromes)
Myasthenia gravis is characterized by fluctuation of muscle weakness in the ocular, bulbar or skeletal muscle districts. Exhaustion is a typical feature of this disorder. Patients may be strong during initial exercise or effort but strength may rapidly decline with repeated exercise. Patients may be strong in the morning and worsen during the day. This is the result of the lack of acetylcholine, the neurotransmitter in the gap junction between motor nerves and muscle which causes muscle contraction. Antibodies against acetylcholine cause a decline in this neurotransimitter which gets ‘used up’ in the junction between nerve and muscle thus causing inability to contract and weakness. The cause is therefore due to a breakdown in the normal communication between nerves and muscles. The clinical picture varies greatly: respiratory, swallowing and skeletal-limb difficulties may occur.