Anti-tuberculosis drug-induced DRESS syndrome in a patient with anti-synthetase syndrome: a diagnostic dilemma

<title>Abstract</title> <p> <bold>Background</bold> The diagnosis of anti-tuberculosis therapy-induced drug reaction with eosinophilia and systemic symptoms (DRESS) syndrome is particularly challenging in patients with underlying autoimmune diseases because of overlapping clinical manifestations and complex medication histories. <bold>Case Presentation</bold> A 58-year-old female patient with anti-synthetase syndrome and soft-tissue tuberculosis developed a “measles-like” eruption 6 weeks after starting anti-tuberculosis therapy. Attributing the clinical presentation to a presumed viral infection resulted in the discontinuation of maintenance corticosteroids, while the causative drugs were continued. This triggered a fulminant progression to exfoliative dermatitis (RegiSCAR score: 5) and delayed, explosive eosinophilia (peak 5.6 × 10⁹/L) following the withdrawal of immunosuppressive control. Despite concurrent maintenance corticosteroids, patch testing revealed robust early reactions to ethambutol at 48h and isoniazid at 96h. <bold>Conclusion</bold> This case report highlights how baseline immunosuppression may induce a pseudo-tolerant state, thereby masking early markers of DRESS syndrome and delaying diagnosis. Importantly, this case demonstrates that patch testing may retain diagnostic utility even under corticosteroid cover, allowing precise culprit identification. This facilitated data-driven sequential drug reintroduction, enabling rifampicin salvage via graded challenge and supporting the successful management of life-threatening infection without compromising autoimmune control. </p>