Ankylosing Spondylitis and Axial Spondyloarthritis

Ankylosing spondylitis is an inflammatory arthritis of the spine and sacroiliac joints. It is not wear and tear, it behaves in the opposite way to mechanical back pain, and the average patient waits years for the diagnosis.

Inflammatory back pain is the opposite of mechanical back pain

This single distinction is what the diagnosis turns on, and it is why the condition is missed. Mechanical back pain is worse with activity and better with rest. Inflammatory back pain does the reverse.

• Worse with rest, better with movement. Patients get up and walk around at 4 a.m. because lying still hurts more than moving.
• Morning stiffness lasting more than 30 minutes, often much longer.
• Night pain, particularly in the second half of the night.
• Onset before age 45, usually gradual rather than after an injury.
• Substantial response to anti-inflammatories — often dramatic, which is itself a diagnostic clue.
• Alternating buttock pain, from the sacroiliac joints.

Someone in their twenties or thirties with months of back pain that eases when they move and wakes them at night does not have a disc problem. That pattern warrants investigation for spondyloarthritis.

What else it affects

Axial spondyloarthritis is a systemic disease, and the features outside the spine are frequently what confirms it:

• Enthesitis — inflammation where tendons attach to bone, classically the Achilles or the plantar fascia. Persistent heel pain in a young adult with back pain is a meaningful combination.
• Uveitis — a painful, red, light-sensitive eye. This is an ophthalmological emergency and needs same-day assessment.
• Peripheral arthritis, usually asymmetric and in the lower limbs.
• Psoriasis or inflammatory bowel disease, which sit in the same family of conditions.
• Dactylitis — a whole finger or toe swollen rather than one joint.

Why it takes years to diagnose

Several things conspire. Early disease frequently shows nothing on plain X-ray — the changes that give the condition its name take years to appear, and a normal film is often read as reassurance. MRI of the sacroiliac joints detects active inflammation far earlier, but it has to be requested.

HLA-B27 is associated with the condition but it is neither necessary nor sufficient. A large number of people carry it and never develop anything, and a meaningful minority of patients are negative. It supports a diagnosis; it does not make or exclude one.

The commonest error is simply attributing it to mechanical back pain in a young, otherwise well person — which is statistically reasonable and, in the presence of the inflammatory pattern above, wrong.

What we can treat

• Sacroiliac joint pain — the joints most consistently involved, and treatable with image-guided injection
• Facet joint pain from the secondary mechanical load of a stiffening spine
• Myofascial pain in the muscles compensating for lost spinal movement
• Physical therapy, which in this condition is genuinely disease-relevant rather than adjunctive — maintaining spinal mobility and chest expansion matters
• Medication review, including the interaction between long-term anti-inflammatory use and everything else

Movement is treatment here

In most back conditions exercise is helpful. In axial spondyloarthritis it is part of the disease management. Regular mobility work, extension-based exercise and maintaining chest expansion measurably influence long-term function, and stopping is genuinely costly.

That is worth knowing because the pain is often worst in the morning, which is exactly when the motivation to move is lowest. Patients who understand why they are doing it tend to keep doing it.

To be assessed, call (314) 310-5577 or text (314) 886-5902. We are at 12174 Natural Bridge Road, St. Louis, MO 63044.

What usually gets missed

The diagnostic delay in axial spondyloarthritis is measured in years, and the reason is that the presentation is the mirror image of what clinicians are trained to expect. Back pain that improves with exercise and worsens with rest reads as implausible to anyone screening for mechanical pain.

It is also missed disproportionately in women, who more often present with neck and peripheral joint involvement and less often with the classic radiographic sacroiliitis. A normal X-ray of the sacroiliac joints does not exclude it — early disease is visible on MRI long before it is visible on plain film.

What to expect over time

Modern treatment has changed the trajectory substantially. The progressive spinal fusion that gave the condition its reputation is far less common in patients treated early with biologic therapy.

Our part is not the disease-modifying treatment, which belongs to rheumatology. It is the mechanical pain that persists alongside it — facet and sacroiliac pain, and the consequences of altered posture — which is treatable in its own right.