Metastatic cancer masquerading as miliary tuberculosis in an immunocompetent young adult.

A healthy, immunocompetent South Asian man in his mid-20s, with a medical history of gastric ulcer, presented to Accident & Emergency with pleuritic chest pain, shortness of breath, fever, night sweats, weight loss, dry cough and asymptomatic iron deficiency anaemia. Following his initial assessment and investigations (chest X-ray, CT and blood tests), a diagnosis of miliary tuberculosis (TB) was made and empirical antimicrobial treatment started. However, subsequent microbiological testing, including urine, blood, induced sputum and lymph node sampling, was negative. Being interpreted as non-diagnostic, the antimicrobial therapy was continued. Following a clinical deterioration while on treatment, the patient's case was re-evaluated and further investigations, including a repeat CT and a liver biopsy, confirmed a diagnosis of stage IV (T1aN3bM1) gastric carcinoma. Our case highlights the diagnostic challenges in differentiating metastatic cancer from miliary TB. We also focus on possible cognitive biases that may have influenced the initial management decisions.