Myasthenic syndromes

Abstract

The neuromuscular junction is vulnerable to autoimmune attack both at the pre-synaptic nerve terminal and at the post-synaptic muscle membrane. Antibodies directed to the nicotinic acetylcholine receptor at the muscle surface are the cause of myasthenia gravis in the majority of cases. Myasthenia gravis is an acquired condition, characterised by weakness and fatigability of the skeletal muscles. The ocular muscles are commonly affected first, but the disease often generalises. Treatment includes symptom control and immunosuppression. The thymus gland plays an important role in the pathogenesis of myasthenia gravis and thymectomy is indicated in certain subgroups. Lambert-Eaton myasthenic syndrome is associated with antibodies directed to the voltage-gated calcium channel antibodies at the pre-synaptic nerve terminal. It is an acquired condition and, in some cases, may be paraneoplastic, often secondary to underlying small cell lung carcinoma. Clinical presentation is distinct from myasthenia gravis, with patients often first presenting with lower limb muscle fatigability and autonomic symptoms. Congenital myasthenic syndromes are inherited neuromuscular disorders due to mutations in proteins at the neuromuscular junction. Various phenotypes exist depending on the protein mutation. Treatment is directed towards symptom control and immunosuppression is not indicated. © 2011 Royal College of Physicians of Edinburgh.