同時發生左腰疼痛及發燒在臨床上常先被認為泌尿道或腎臟感染。本案是一位47歲男性病患，因左側腰痛併發燒初診斷為急性腎盂腎炎。但經電腦斷層發現腎梗塞，之後經仔細評估發現有心雜音、手指結節（Osler’s node）與施打海洛因病史，經心臟超音波檢查後，確立診斷為二尖瓣心內膜炎，接受靜脈注射Oxacillin sodium治療後獲得改善。因此，臨床上若腎盂腎炎經抗生素治療未改善，需有影像學檢查以排除其他可能性，若發現腎梗塞合併心雜音或手指結節等相關症狀，需高度懷疑感染性心內膜炎之可能性。

Simultaneous left flank pain and fever are often initially attributed to urinary tract infections or pyonephritis. This case is on a 47-year-old man who was first diagnosed with acute pyelonephritis due to having left back pain and fever for 2 days. However, after renal infarction was found through kidney computed tomography (CT), he was then carefully assessed and found to have heart murmur, finger nodules (Osler’s node), and a history of heroin addiction. Infective endocarditis was then considered and confirmed by echocardiogram. After receiving Oxacillin sodium treatment, the patient’s condition improved. Therefore, if the clinical symptoms of pyonephritis do not improve after antibiotic therapy, further image study is necessary to rule out other possibilities. If the image study shows renal infarction, we should carefully assess whether the patient has heart murmur, skin lesions, or drug addiction history. If so, infective endocarditis should be highly suspected.