Lambert-Eaton syndrome

- autoimmune disorder caused by antibodies against the voltage-sensitive calcium channels of the motor nerve terminals
- males more than female, with underlying malignancy (majority small lung lung CA)
- typically presents with weakness improved with exercise
- reduced/absent reflex (cardinal sign), because less transmitter is released, but reflexes may increase after maximum voluntary contraction (post-tetanic potentiation)
- also presents with autonomic symptoms (dry mouth)
- nerve conduction studies: compound motor action potential have small amplitude which after exercise or with repetitive stimulation will immediately increase by 100%
- voltage gated calcium channel antibodies are seen in almost 100% of LEMS patient with cancer and 90% of LEMS patient without cancer
- treatment: 3-4 diaminopyridine 20mg 5 times/day (potassium channel blocker, which helps maintain depolarisation of the nerve terminal by preventing repolarisation, leading to more calcium enter nerve terminal) or IVIG