Clinical reasoning: a 39-year-old man with abdominal cramps.

SECTION 1 A 39-year-old lawyer presented with intermittent spasms and pain in his abdominal muscles, particularly the right upper quadrant. These had occurred since his mid-20s and there had been long asymptomatic periods, including 8 years prior to the most recent 4-month exacerbation. Trivial movement triggered a spasm of the abdominal muscles, leading to severe pain, which made breathing uncomfortable and interfered with sleep. The symptoms subsided spontaneously after 4 to 5 days, leaving him with a sore abdomen for several weeks. Past attacks had also been precipitated by specific forms of repetitive exercise such as jogging. He described ill-defined numbness in the left leg, but denied any muscle twitching, weakness, back pain, or sphincter disturbance. There was no significant past medical or family history. On examination, cranial nerves were unremarkable. Tone and power were normal in upper and lower limbs. Tendon reflexes were brisk throughout, particularly in the lower limbs, where they were brisker on the left than the right; plantar responses were flexor. Abdominal reflexes were brisk on the right and absent on the left (video on the Neurology® Web site at www. neurology.org). No fasciculations or myokymia were seen throughout. There was no demonstrable sensory asymmetry or loss to any modality in the lower limbs. Gait and cerebellar function were normal.