Lambert Eaton Myasthenic Syndrome (LEMS) is an autoimmune disorder affecting the neuromuscular junction caused by antibodies against voltage gated calcium channel antibodies. The neurophysiological hallmark of LEMS is incremental response to repetitive nerve stimulation, especially at high frequency stimulation.
A 54-year-old gentleman presented to the Neurology clinic with a 9-month history of progressive walking difficulty. He had difficulty standing up from a sitting down position and the symptoms were worse towards the end of the day. He had a transient history of dry mouth when the symptoms started, but denied any postural dizziness, sweating or bowel/bladder symptoms. He denied having any double vision, droopy eyelids, speech or swallowing symptoms. He had lost 1.5 stones in weight over the preceding 7–8 months. Examination showed proximal muscle weakness with reduced reflexes, which could not be potentiated. A clinical suspicion of LEMS was made, but the neurophysiological examination (repeated on three occasions) showed consistently decremental response at low and high frequency stimulations.
The VGCC antibody was positive (293, normal 0–45), confirming the clinical suspicion of LEMS. The AChR and MuSK antibodies were negative.
This is an unusual neurophysiological finding of a decremental response in a patient with clinical and immunological evidence of LEMS.