Pyrexia of unknown origin

Pyrexia of Unknown Origin (PUO) is defined as a fever ≥38.3°C (101°F) lasting for more than 3 weeks, in which the cause remains undiagnosed even after appropriate evaluation. The common causes include infections (most common), malignancies, connective tissue disorders, and miscellaneous conditions, while some cases remain idiopathic. Evaluation requires a systematic approach with detailed history, clinical examination, and targeted investigations to identify the underlying cause.