Pyridostigmine

Myasthenia gravis is an autoimmune disease involving dysfunction at the neuromuscular junction most commonly due to autoantibodies directed against the acetylcholine receptor (AChR), but also against other targets such as the muscle-specific kinase (MUSK), lipoprotein-related protein 4 (LRP4), or agrin. In the case of AChR antibodies, AChRs are directly bound and cross-linked, impairing acetylcholine binding and contributing through various mechanisms to receptor degradation. The lack of acetylcholine signalling leads to muscle tone loss, muscle weakness, and fatigue.

Pyridostigmine is a reversible acetylcholinesterase inhibitor that increases extracellular acetylcholine levels in the neuromuscular junction by impairing its breakdown by acetylcholinesterase. The increased acetylcholine leads to increased neural transmission across the junction, which drastically improves myasthenia gravis symptoms.

In addition to its use in myasthenia gravis and in reversing neuromuscular blocks, pyridostigmine is also a common first-line treatment in congenital myasthenic syndromes (CMS), of which there are multiple subtypes caused by mutations in more than 30 distinct genes. CMS present similarly to myasthenia gravis, albeit due to distinct underlying causes, and often benefit from pyridostigmine. However, in some subgroups, treatment with pyridostigmine is detrimental; detailed genetic testing is required before starting therapy.