Autoimmune neurological diseases

Myasthenia gravis (MG) is one of the best understood autoantibody-mediated disorders. The pathogenic antibodies against the acetylcholine receptor (AChR) have been well characterized and are known to impair neuromuscular transmission by direct blockade, complement mediated damage and accelerate receptor-mediated endocytosis. The clinical presentation is characterized by fatiguable weakness with a predilection for the extra-ocular, facial, bulbar, respiratory and proximal limb muscles. Diagnosis is confirmed by the presence of antibodies against the AChR or muscle-specific kinase in the serum. Electrophysiology demonstrates a decrement on repetitive nerve stimulation and increased jitter on single-fibre studies. Symptomatic relief is attained with an acetylcholinesterase inhibitor, pyridostigmine, but definitive treatment requires immunosuppressive drugs. Thymectomy is indicated for 10-15% of patients who have thymomas and may be indicated in young patients with AChR antibodies to try to improve their MG. Lambert-Eaton myasthenic syndrome is associated with small cell lung cancer in 50% of patients, particularly smokers. Immunosuppressive treatment regimes are similar to those used in MG, but 3,4-diaminopyridine is used for symptomatic relief. Limbic encephalitis associated with antibodies to voltage-gated potassium channel antibodies (VGKC) is a newly described disorder characterized by the subacute onset of short-term memory loss, seizures and confusion. Investigations reveal low serum sodium, high signal in the hippocampi on magnetic resonance imaging, a high titre of VGKC antibodies, and anterograde and retrograde memory loss on neuropsychological assessment. Patients respond very well to prolonged treatment with high-dose steroids. © 2008 Elsevier Ltd. All rights reserved