19th June 2023

A 29-year-old-man presents to A&E with severe left-sided headaches with constant tearing of left eye, drooping of his eyelid, sweating and rhinorrhoea

A 29-year-old-man presents to A&E with severe left-sided headaches with constant tearing of left eye, drooping of his eyelid, sweating and rhinorrhoea. He has had similar attacks of excruciating bouts of pain more than 15 times today, each only lasting 5-10 minutes. He has no significant past medical history. On examination, he has left partial ptosis with associated miosis. There is no focal neurology. CT head was normal.

Which one of the following options is the most likely aetiology for his headache?