Navigating a Diagnostic Dilemma: A Case Report of Overlapping Presentation of Granulomatosis With Polyangiitis and Tuberculosis.

Granulomatosis with polyangiitis (GPA) and tuberculosis (TB) present a diagnostic conundrum due to their similar clinical manifestations, histopathological features, and the presence of positive antineutrophil cytoplasmic antibodies (ANCAs) in both conditions. We present the case of a 54-year-old patient who was initially evaluated for TB but developed a vasculitic rash during the course of the illness, suggesting an alternative diagnosis. Further evaluation revealed positive cytoplasmic ANCA (C-ANCA) and pulmonary nodules with cavitations on chest imaging, shifting the diagnosis toward GPA. The diagnosis of GPA was confirmed based on the EULAR/ACR (European League Against Rheumatism/American College of Rheumatology) 2022 classification criteria. Disease remission was induced with steroid pulse therapy and intravenous cyclophosphamide. Azathioprine was used for maintenance therapy. The patient made a remarkable recovery with treatment. We discuss this case due to the scarcity of reported cases in Sri Lanka to provide insight into the diagnostic approach for patients presenting with similar clinical phenotypes. Although TB is more common than GPA in Asian countries, few cases have been reported with overlapping features of both diseases. In light of this diagnostic dilemma, clinicians are faced with significant challenges in accurately distinguishing between the two diseases, which could lead to delays in the establishment of appropriate treatment and management. Therefore, we highlight the importance of considering GPA as a differential diagnosis for TB, even in Asian countries.