Ordinary back pain fades after a night in bed. The back pain of ankylosing spondylitis, a chronic inflammatory arthritis of the spine, does the opposite. It flares during rest and eases once you start moving.
That reversal is one of the clearest clinical clues, described by the Arthritis Foundation and by the National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS). Yet the condition is widely missed. In a US survey of adults living with AS, only about 37 percent were diagnosed within a year of seeking medical attention, while roughly a third waited a decade or more.
Ankylosing spondylitis is uncommon but not rare. The NIH-hosted StatPearls clinical reference puts US prevalence at around 0.2 to 0.5 percent of adults, in the neighborhood of 1 in 200 to 1 in 500 people.
Below are seven signs, drawn from the Arthritis Foundation and NIH resources, that distinguish inflammatory back pain from an everyday sore back.
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1. Pain that worsens with rest
Mechanical strain typically calms down when you lie still. AS pain does the opposite. StatPearls lists "lack of improvement with rest" and nocturnal pain that eases on getting up as core features of inflammatory back pain.
2. Morning stiffness that lingers
Stiffness after waking that takes more than roughly 30 minutes to loosen up is a hallmark. NIAMS notes that symptoms "may be worse in the morning or after periods of inactivity."
3. Symptoms starting before age 45
AS is a young person's disease. Roughly 80 percent of patients develop their first symptoms before age 30, and fewer than 5 percent are diagnosed after 45, according to StatPearls. New back pain in a person in their 20s or 30s is a much stronger red flag than the same pain in someone in their 60s.
4. Fatigue out of proportion to activity
Chronic inflammation drains energy. The Arthritis Foundation lists fatigue, appetite loss, and low-grade fever among typical AS symptoms, distinct from the tiredness that follows a busy day.
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5. Alternating buttock pain
Pain that shifts from one side of the lower back or buttock to the other reflects inflammation of the sacroiliac joints, where the spine meets the pelvis. It is a classic early clue in axial spondyloarthritis and often predates any visible change on X-ray.
6. Reduced spinal flexibility
Over time, inflammation stiffens the spine and cuts the range of motion in the lower back and rib cage. Rheumatologists use simple bend-and-reach tests to spot this loss during a physical exam.
7. Red or painful eyes
AS can inflame the front of the eye, a condition called uveitis. NIAMS describes chronic eye inflammation that "causes dryness, pain, redness, sensitivity to light and vision problems." StatPearls estimates that acute anterior uveitis shows up in about 25 to 35 percent of AS cases and can be the symptom that finally sends someone to a specialist.
When to ask for a rheumatologist
If three or more of these signs apply and back pain has persisted for more than three months, it is worth asking a primary care doctor for a referral to a rheumatologist. The standard next steps are an HLA-B27 blood test, which looks for a genetic marker strongly linked to AS, and an MRI of the sacroiliac joints. StatPearls notes that MRI can pick up sacroiliitis, inflammation of those joints, years before it becomes visible on a plain X-ray.
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This article is made and published by Jesper Bengtson, who may have used AI in the preparation.