Ankylosing spondylitis

Chronic inflammatory disease of the axial skeleton, primarily involving the sacroiliac joints and spine, leading to pain and progressive fusion (ankylosis) of vertebrae (late-stage "bamboo spine"). Strongly associated with HLA‑B27 (present in ~90% of cases) and one of the prototypical seronegative spondyloarthritides.

• AS often begins in the 20s-30s and can cause severe spinal deformity, chest restriction, and disability if untreated. Early recognition (distinguishing from common back pain) allows treatment to reduce pain and preserve mobility. It's a classic "young man with back pain" exam case, and features like uveitis or Achilles enthesitis commonly show up in questions.

• Typical patient: young male (<40) with chronic low back and buttock pain. Pain and pronounced morning stiffness improve with exercise and worsen with rest. Symptoms often start at the sacroiliac joints (deep buttock pain, sometimes alternating sides) and ascend the spine.
• Limited spinal mobility on exam: positive Schober test (limited lumbar flexion). As disease progresses, loss of lumbar lordosis and thoracic kyphosis develop, leading to a stooped posture. Reduced chest wall expansion due to costovertebral joint involvement (may cause mild restrictive lung impairment).
• Enthesitis is common: Achilles tendon insertion pain, plantar fasciitis, or costosternal junction pain. ~25-40% have acute anterior uveitis episodes (unilateral eye pain/redness/photophobia). Peripheral arthritis (hips, shoulders, knees) occurs in some, but axial skeleton is dominant.
• Lab clues: HLA-B27 positive in most patients; ESR/CRP often elevated. No rheumatoid factor (seronegative).
• Imaging: X-ray of pelvis shows bilateral sacroiliitis (erosions and sclerosis in SI joints) early. As AS advances, syndesmophytes (bony bridges between vertebrae) form, leading to the classic "bamboo spine" appearance on spinal X-ray (diffuse vertical ossification).

1. Check lumbar flexion: Schober test (mark 10 cm above and 5 cm below the lumbar dimple, then have patient bend forward – in AS, the distance increases <5 cm, indicating restricted flexion). Limited chest expansion (<2.5 cm difference between full inhale and exhale at nipple line) also suggests advanced AS.
2. Imaging confirmation: X-ray of sacroiliac joints is the cornerstone – look for erosions, pseudowidening, then sclerosis and fusion. If X-ray is equivocal and suspicion is high, get an MRI for active inflammation in SI joints (useful in early disease). Spinal X-rays in later disease show syndesmophytes and fusion of facet joints.
3. Distinguish from mechanical back pain: AS starts young and improves with exercise; mechanical (disc degeneration) usually in older patients and worse with activity. Also, AS often has night pain (second half of night) and buttock pain, whereas mechanical pain improves when supine.
4. Be aware of extras: a history of uveitis strongly supports AS in a back pain patient. Chronic inflammatory bowel disease can also cause a similar spondylitis, but in idiopathic AS, bowel symptoms are absent (however, up to 5-10% of AS patients have subclinical gut inflammation).
5. Monitoring: assess spinal mobility over time (tragus-to-wall distance for cervical kyphosis, chest expansion, etc.). If a patient with established AS reports a sudden focal increase in pain or neurologic changes, evaluate immediately for spinal fracture (fused spines are fragile).

1. Exercise and daily stretching to maintain posture and mobility (very important).
2. NSAIDs (e.g., indomethacin) are first-line medications; they often provide significant relief and may slow radiographic progression in some cases. Patients may take them regularly at anti-inflammatory doses.
3. TNF-α inhibitors (e.g., etanercept, infliximab) or IL-17 inhibitors (secukinumab) are indicated for active disease not controlled by NSAIDs. These biologics can reduce symptoms and possibly slow disease progression (important as conventional DMARDs like methotrexate do not help axial disease).
4. For peripheral arthritis in AS, sulfasalazine can be tried (especially if there is coexistent IBD), though it has modest effect. Local corticosteroid injections can help enthesitis or a badly inflamed joint, but systemic steroids are generally avoided (ineffective for axial symptoms).
5. Advanced deformities (e.g., severe kyphosis) may require surgical intervention (spinal osteotomy) in select cases. Encourage patients to avoid smoking (which can worsen chest expansion issues and osteoporosis) and ensure adequate osteoporosis screening/treatment since ankylosed spines are prone to fracture.

• Bamboo spine on X-ray = classic late-stage ankylosing spondylitis (ossified spinal ligaments).
• Limited chest expansion in a young patient → think AS (costovertebral joint fusion).
• The question mark posture (flexed neck and kyphosis) in advanced AS results from spinal fusion and cannot be corrected by effort.
• HLA-B27 is not required for diagnosis, but a positive result in a young person with inflammatory back pain bolsters confidence.

• New neurologic deficit (weakness, bowel/bladder dysfunction) in an AS patient → evaluate urgently for cauda equina syndrome or spinal cord compression (could be from fracture or atlantoaxial subluxation).
• AS patients have increased risk of spinal fractures even with minor trauma (due to rigid, osteoporotic spine) – any acute localized spinal pain after injury should prompt immediate imaging.
• Night sweats, fever, weight loss in a patient with AS → consider that infection (e.g., vertebral osteomyelitis/TB) or malignancy could be superimposed; do not attribute these systemic signs to AS flares.

1. Young adult with inflammatory back pain → suspect AS; test HLA-B27 and inflammatory markers.
2. Do pelvic X-ray: if sacroiliitis present, diagnosis is strongly supported. If X-ray normal but suspicion remains, get MRI of SI joints.
3. Diagnose AS based on modified New York criteria: (1) clinical – low back pain >3mo improved by exercise, limited lumbar motion, limited chest expansion; plus (2) radiologic – sacroiliitis on imaging. HLA-B27 positivity can help but is not required.
4. Begin NSAIDs and exercise therapy; educate patient on posture and stretching. If no improvement or high disease activity, escalate to a TNF inhibitor (or IL-17 inhibitor).
5. Monitor spinal mobility and symptoms regularly. Ensure osteoporosis prevention (calcium/Vit D, consider bisphosphonates) because of fracture risk. Advise on fall precautions and neck support as needed, given risk of spinal injury.

• 30-year-old man with chronic low back pain/stiffness that improves during the day, and X-ray showing bilateral sacroiliac fusion → Ankylosing spondylitis.
• Long-standing AS patient with fused spine (bamboo spine) presents with acute neck pain after minor fall → suspect a fracture in the fused spine.
• Young man with low back pain and unilateral eye pain/blurry vision (uveitis) → Ankylosing spondylitis (extra-articular uveitis).