Back Pain with Sacroiliac Tenderness

🗒️ Question

A 28 year old man presents with 18 months of lower back pain that is worse in the morning and improves with activity. He reports stiffness lasting over an hour upon waking. He has no bowel or bladder symptoms. His father was diagnosed with Ankylosing Spondylitis.

On examination, there is reduced forward flexion of the lumbar spine, and Schober’s test is positive. Tenderness is noted over the sacroiliac joints bilaterally. Neurological examination of the lower limbs is normal.

Which is the most appropriate investigation to confirm the diagnosis?

(A) Blood test for HLA-B27

(B) ESR

(C) MRI of the sacroiliac joints

(D) Plain X-ray of the lumbar spine

(E) Ultrasound of the sacroiliac joints