HLA-B27, Mantoux Test, and Eosinophil Count: Help in the Diagnosis of Reactive Arthritis Due to Tubercular Hypersensitivity

Reactive arthritis (ReA) is a form of inflammatory arthritis usually triggered by gastrointestinal/genitourinary infections. We present the case of a middle-aged man with HLA-B27-associated ReA and tuberculosis (TB) hypersensitivity, manifesting as polyarthritis, inflammatory low back pain, and pleural effusion. The patient had a three-year history of progressive joint pain, initially involving the knees, followed by the bilateral ankle joints and small joints of the hands, wrists, shoulders, elbows, and axial skeleton. He also had a prolonged fever with an exudative pleural effusion, eosinophilia, and Mantoux positivity, though pleural fluid adenosine deaminase (ADA) and cartridge-based nucleic acid amplification test (CBNAAT) were within normal limits and negative, respectively. Due to the autoimmune-inflammatory overlap, treatment with nonsteroidal anti-inflammatory drugs (NSAIDs) resulted in rapid improvement in joint pains, and tuberculosis preventive therapy was initiated to prevent TB reactivation. The case highlights the complex interaction between immune-mediated inflammation and TB hypersensitivity, emphasizing the need for careful differential diagnosis and treatment plans in seronegative arthritis with systemic features.