The term “myasthenia” comes from the Latin “myos” meaning muscle, and the Greek asthenes, meaning a- (without) + sthenos (strength), and so it literally means muscle weakness, not fatiguable weakness. In common parlance, however, the term “myasthenic weakness” is used to describe the fatiguability which is a cardinal feature of myasthenia gravis, an acquired, autoimmune, post-synaptic disorder. In 1956 Lambert, Eaton and Rooke described a novel acquired pre-synaptic neuromuscular transmission disorder which has become referred to as the Lambert–Eaton myasthenic syndrome or LEMS. Indeed, it is described as a “myasthenic” syndrome in textbooks alongside myasthenia gravis but, potentially confusingly, it is not usually characterised by prominent complaints of fatiguable weakness and the clinical picture is unlike conventional myasthenia gravis. This commonly leads to diagnostic delay in a treatable disorder.

A CASE

A woman presented at the age of 32 years. She gave a four-year history of bilateral knee pain and had thought this was the explanation for her decreasing mobility requiring her to resort to sticks to walk, and for the past six months the use of a wheelchair out of doors. She had a past history of chondromalacia patellae and presumed this to be the cause of her pain. She did not give any story of variability in muscle strength or fatiguability. There was no upper limb weakness, or bulbar features. She had difficulty rising from a chair and was unable to get out of a bath. There were no sensory symptoms. She was referred from …