A 68-year-old man came to the emergency department complaining of left-side thoracic back pain, after 5 days of outpatient treatment with analgesics did not help him. His pain started after physical labor, but he did not recall any trauma. A review of his medical history revealed only coronary artery disease, with coronary stent placement several years before this event. He had not been hospitalized recently, undergone an invasive procedure, or taken antibiotics.
On examination, a left thoracic paraspinal muscle was tender without fluctuance, overlying skin redness, or a lesion. An elevated white blood cell count of 12,300/mcL was the only laboratory test with abnormal results. The patient did not have fever, and results of urinalysis, chest radiograph, and abdominal sonogram were normal. Computed tomography (CT) images of the abdomen and pelvis showed inflammation of a left thoracic paraspinal muscle.
Thirty-six hours after admission, the patient developed fever (38.8°C). His physicians obtained a blood culture. The fever recurred (at 38.9°C) the following day, and 2 more blood cultures were done. His back pain did not improve despite analgesics, intravenous antibiotics, and physical therapy; therefore, on the eighth day in the hospital, magnetic resonance imaging (MRI) was performed (FIGURE).
FIGURE
MRI of the back
What is the diagnosis?