In ankylosing spondylitis, night pain is most common during which portion of the night?

• A. First half of the night
• B. Afternoon
• C. Second half of the night
• D. Early morning after waking

Answer: (C)

Inflammatory back pain from ankylosing spondylitis tends to worsen during rest at night, with the strongest nocturnal pain occurring in the latter part of sleep. This late-night pattern is tied to circadian fluctuations in inflammatory activity and the reduced anti-inflammatory effect as the night progresses, so patients often wake from sleep due to pain in the second half of the night. Morning stiffness after waking is common and improves with movement, but the peak nocturnal pain is typically in the second half of the night, not in the first half, the afternoon, or immediately after waking.