MRCP2-4588

MRCP2-4588

A 67-year-old woman presents to the Rheumatology Clinic for evaluation. She has been experiencing progressive back pain for the past 3 years and now reports a burning pain that radiates down from her buttocks into both legs when she walks only a short distance, causing her to have to sit and rest until the pain subsides. She smokes 6 cigarettes per day and has a history of osteoarthritis and hypertension. On examination, her blood pressure is 140/90 mmHg; pulse is 75/min and regular. Her ABPI is 0.98. Lumbar spine movement is limited by pain and stiffness. Straight leg raise is normal.
Investigations:
Hb 129 g/l
WCC 6.8 x109/l
PLT 179 x109/l
Na+ 138 mmol/l
K+ 4.2 mmol/l
Creatinine 98 micromol/l
ESR 12 mm/1st hour
Lumbar spine x-ray shows evidence of bilateral facet joint arthritis and disc space narrowing.
What is the most likely diagnosis?