Paraneoplastic or autoimmune neuromuscular transmission disorders

**Definition:** NMT disorders are defined by a variable disturbance of the function of the neuromuscular transmission, resulting in fluctuating muscle weakness and fatigue. These are usually classified into pre- and postsynaptic disorders.

Presynaptic disorders, mainly the Lambert Eaton Myasthenic Syndrome (LEMS) is associated with antibodies targeting the voltage gated calcium channels (PQ and N type). LEMS is associated with malignancy (pulmonary or extra-pulmonary small cell carcinoma) in about 50% of cases. In the context of LEMS the detection of SOX 1 (anti glial nuclear) antibodies is highly predictive of cancer.

Postsynaptically, myasthenia gravis is mostly (> 90%) associated with antibodies targeting the muscle acetylcholine receptor (AChR) or rarely other proteins (including muscle -specific kinase -MuSK). Myasthenia is usually not considered a paraneoplastic disease, with the exception of thymoma in about 10% cases.