HLA B27 Positive Seronegative Knee Arthritis: A Rare Case Report

HLA-B27 POSITIVE SERONEGATIVE KNEE ARTHRITIS: A RARE CASE REPORT Dr. Juhi Shahab, Dr. A. K. Yadav, Dr. Rashmi Arora Department of Pathology, Vardhman Mahavir Medical College and Safdarjang Hospital, New Delhi, 110029 Introduction: Human leukocyte antigen B27 (HLA-B27) is a class I surface antigen encoded by the B locus in major histocompatibility complex on chromosome 6 and presents antigenic peptides to T cells. HLA-B27 is strongly associated with ankylosing spondylitis. When a patient tests negative for Rheumatoid factor (RF) and Anti-cyclic citrullinated peptide (anti-CCP antibodies), still display symptoms consistent with arthritis, they are given a diagnosis of seronegative arthritis. Incidence rate is 22/100, 000cases/year. Our case is a rare form of seronegative HLA-B27 positive arthritis. Case Report: A 15year old male presented with swelling and pain in left knee and left ankle since many years. The TLC and ESR were raised. RF and anti-CCP antibodies were negative, HLA-B27 was positive. X-ray knee joint findings were nonspecific, MRI left ankle reveals mild joint effusion. A biopsy from left knee containing multiple grey brown soft tissue pieces measuring 0.5x0.5x0.2cm, microscopically showed fragments of synovial tissue with extensive fibrin deposition, mild to moderate mixed inflammatory cell infiltrate comprising of neutrophils and lymphocytes. Based on clinical picture, histological and radiological findings a final diagnosis of HLA-B27 positive seronegative arthritis was given. Conclusion: Spondyloarthritis is suspected whenever a young patient (less than 40 years) presents, with inflammatory low back pain, and asymmetrical involvement of knees or ankles. Thus, it is required to correlate the clinico-radiological profile of the patient before giving a final report as nonspecific arthritis on synovial biopsies.