Co-existing Ankylosing Spondylitis and Rheumatoid Arthritis in a Patient Undergoing Total Knee Arthroplasty Under Peripheral Nerve Blocks.

Introduction: While laboratory tests and clinical criteria are well-defined, simultaneous presence of concomitant symptoms can lead to a misdiagnosis and delay in initiation of appropriate pharmacotherapy. Similarly, natural joint disease progression may also vary and present with atypical presentations. Case Report: Here we report a case of Ankylosing Spondylitis (AS) with Rheumatoid Arthritis (RA) proven clinically, radiologically, as well as serologically, in whom multiple joint replacement procedures were performed. The association between these two conditions with overlapping features and laboratory markers constitutes an interesting phenomenon and can pose a diagnostic dilemma, thus, increasing the importance of awareness and early diagnosis of this co-existence. We report the case of a 63 year-old gentleman who was a known case of ankylosing spondylitis since the age of 38. The patient had undergone a staged bilateral total hip arthroplasty 18 years ago and presented to us with knee arthritis necessitating Total Knee Arthroplasty. The patient was subsequently diagnosed to have coexisting Rheumatoid Arthritis. After a failed attempt for spinal anaesthesia, a para-sacral sciatic block in the lateral position and an infra-inguinal femoral nerve block and obturator nerve block in the supine position were given under ultrasound guidance. The total knee replacement was performed successfully without any intra-operative complications. Conclusion: This combined entity requires accurate assessment or can be easily misleading. No definite conclusion is possible with regards to the etiopathogenesis of these conditions coexisting but this association with overlapping features and laboratory markers constitutes an interesting phenomenon and can pose a diagnostic dilemma.