Child who presents with inflammatory back pain (worse upon waking in morning) with involvement of sacroiliac joint and decreased flexion at waist (2 features that are highly associated/specific for ankylosing spondylitis) and elevated ESR (further supporting inflammatory back pain) with imaging showing vertebral body squaring and fusion of sacroiliac joint, most consistent with ankylosing spondylitis
Key idea: Back pain that is worse upon waking in morning = Inflammatory back pain = PAIR diagnoses: Psoriatic arthritis, Ankylosing spondylitis, Inflammatory bowel disease, Reiter/Reactive arthritis (at least on NBME exams)
submitted by โjesusisking(31)
I believe the vertebrae toward the bottom are fused corresponding to the boy's low-back pain and the diagnosis