Review Question - QID 214332

A 65-year-old man presents to the clinic with complaints of back pain. His past medical history is significant for diabetes, hypertension, benign prostatic hyperplasia, and anxiety. He was recently hospitalized for streptococcal bacteremia from pneumonia but has recovered from that illness. The patient reports progressively worsening back pain that began 5 weeks ago shortly after he lifted some heavy groceries. The pain is concentrated at the lower back and is described as crampy and dull in quality. It waxes and wanes but is especially worse at night. He denies any urinary incontinence, fevers, sensory changes, or weakness. A physical examination is significant for tenderness at the lumbar spine. A straight leg test is negative, and the patient has no sensory or motor deficits. Laboratory studies are shown below. A radiograph of the lumbar spine is obtained and shown in Figure A.

Hemoglobin: 11.2 g/dL
Hematocrit: 32%
Leukocyte count: 7,600/mm^3 with normal differential
Platelet count: 136,000/mm^3

Serum:
Na+: 137 mEq/L
Cl-: 98 mEq/L
K+: 3.8 mEq/L
HCO3-: 24 mEq/L
Ca2+: 12.8 mg/dL
BUN: 24 mg/dL
Glucose: 101 mg/dL
Creatinine: 1.0 mg/dL
Alkaline phosphatase: 124 U/L
Aspartate aminotransferase (AST, GOT): 17 U/L
Alanine aminotransferase (ALT, GPT): 12 U/L

What is the most likely explanation for this patient’s symptoms?