Review Question - QID 212578

A 33-year-old man presents to the emergency department with back pain. He is currently intoxicated but states that he is having severe back pain and is requesting morphine and lorazepam. The patient has a past medical history of alcohol abuse, drug seeking behavior, and IV drug abuse and does not routinely see a physician. His temperature is 102°F (38.9°C), blood pressure is 127/68 mmHg, pulse is 120/min, respirations are 17/min, and oxygen saturation is 98% on room air. Physical exam is notable for tenderness over the thoracic and lumbar spine. The pain is exacerbated with flexion of the spine. The patient’s laboratory values are notable for the findings below.

Hemoglobin: 12 g/dL
Hematocrit: 36%
Leukocyte count: 16,500/mm^3 with normal differential
Platelet count: 197,000/mm^3

Serum:
Na+: 139 mEq/L
Cl-: 100 mEq/L
K+: 4.3 mEq/L
HCO3-: 25 mEq/L
BUN: 20 mg/dL
Glucose: 99 mg/dL
Creatinine: 1.1 mg/dL
Ca2+: 10.2 mg/dL
CRP: 35.2 mg/L

Further imaging is currently pending. Which of the following is the most likely diagnosis?