Review Question - QID 213659

A 33-year-old man presents to the emergency department with back pain. The patient states that his pain started yesterday and has been gradually worsening. He also states that lately he has generally felt weak and ill. The patient has a past medical history of alcohol abuse, IV drug abuse, and antisocial personality disorder. He is currently requesting IV diphenhydramine and hydromorphone. His temperature is 101°F (38.3°C), blood pressure is 102/78 mmHg, pulse is 101/min, respirations are 19/min, and oxygen saturation is 99% on room air. Physical exam is notable for focal tenderness over the lumbar spine. Otherwise, the patient’s neurological and musculoskeletal exams are within normal limits. Laboratory values are ordered as seen below.

Hemoglobin: 12 g/dL
Hematocrit: 36%
Leukocyte count: 11,500/mm^3 with normal differential
Platelet count: 397,000/mm^3

Serum:
Na+: 137 mEq/L
Cl-: 103 mEq/L
K+: 4.8 mEq/L
HCO3-: 25 mEq/L
BUN: 24 mg/dL
Glucose: 79 mg/dL
Creatinine: 1.1 mg/dL
Ca2+: 10.2 mg/dL
ESR: 49 mm/hr
AST: 202 U/L
ALT: 101 U/L

The patient threatens to leave if he does not receive IV pain medications. Which of the following is the most likely diagnosis?