Thinking beyond Tuberculosis: Pulmonary Nocardiosis by Nocardia farcinica in a Patient with Autoimmune Hepatitis

Nocardiosis is a rare but serious infection caused by Nocardia species (class Actinobacteria, order Corynebacteriales). Nocardia is commonly found in soil, dust and plant material, and the infection primarily affects immunocompromised individuals, most often presenting as Pulmonary Nocardiosis (PN) via inhalation. It requires a prolonged course of antimicrobials and is a significant cause of mortality in such patients. PN is often misdiagnosed as Tuberculosis (TB) due to overlapping features, delaying diagnosis and treatment. This case describes a 44-year-old male, a known case of autoimmune hepatitis on corticosteroid therapy, who presented with clinical and radiological features suggestive of pulmonary TB. Modified Kinyoun staining of pleural fluid showed acid-fast, branched, filamentous bacilli and culture grew yellow, chalky colonies identified as Nocardia farcinica. The organism was also isolated on automated and conventional mycobacterial culture media. The patient was successfully treated with cotrimoxazole (double strength). This emphasises the need to include Modified Ziehl-Neelsen (ZN) stain as a rapid screening test to rule out PN and avoid treatment with Antitubercular Therapy (ATT).