Differential diagnosis of optic neuritis in a patient with ankylosing spondylitis.

The authors report a 38-year-old white man with ankylosing spondylitis (AS) who presented with recurrent ischaemic optic neuritis. The initial diagnosis was of multiple sclerosis, but further investigation showed serology and cerebrospinal fluid culture positive for syphilis. After treatment for tertiary syphilis with penicillin, there was complete remission of the ocular symptoms. This case illustrates the differential diagnosis of optic neuritis in AS and supports the relevance of investigating infectious diseases in the management of ischaemic optic neuritis.