Atlantoaxial dislocation as the presenting symptom of ankylosing spondylitis.

A 27-year-old woman presented with nontraumatic atlantoaxial dislocation that required a C1-C2 fusion. A comprehensive investigation initially failed to reveal any evidence of infectious or rheumatologic disease and she remained well for 3 1/2 years, at which time a diagnosis of ankylosing spondylitis was established. There are no other similar cases reported in the medical literature. When dealing with a patient who has experienced a spontaneous atlantoaxial dislocation, a thorough assessment looking for an underlying infectious or inflammatory etiology is mandatory. Furthermore, the authors recommend that any patient who has negative investigations be followed long-term; an underlying covert inflammatory cause may only become evident after significant delay.