High Quality Content by WIKIPEDIA articles! Lambert–Eaton myasthenic syndrome (LEMS, sometimes Lambert–Eaton syndrome or Eaton–Lambert syndrome) is a rare autoimmune disorder that is characterised by muscle weakness of the limbs. It is the result of an autoimmune reaction, where antibodies are formed against voltage-gated calcium channels in the neuromuscular junction (the connection between nerves and the muscle that they supply). Around 60% of those with LEMS have an underlying malignancy, most commonly small cell lung cancer; it is therefore regarded as a paraneoplastic syndrome (a condition that arises as a result of cancer elsewhere in the body).