Pseudo-septic hip arthritis as the presenting symptom of ankylosing spondylitis: a case series and review of the literature.

INTRODUCTION Ankylosing spondylitis (AS) typically presents with inflammatory back pain and stiffness, but severe hip involvement may also be present. In this study, we evaluated the frequency of severe hip arthritis mimicking septic arthritis as initial presenting symptom of AS. METHODS Utilising billing records, we retrospectively studied all AS patients seen from the years 2006 to 2009 at our institution. The primary endpoint was severe hip arthritis mimicking septic arthritis as the initial presenting symptom of AS. RESULTS A total of 121 AS patients were identified from billing records, of whom 3 had severe hip arthritis mimicking septic arthritis as the initial presenting symptom of ankylosing spondylitis. CONCLUSIONS Our study highlights the importance of including AS in the differential diagnosis of severe acute inflammatory hip arthritis in young adults, even when the onset appears to be abrupt.