Spondyloarthropathies

Inflammatory back pain is the cardinal feature of axial SpA: onset before age 40, insidious (not traumatic) onset, duration over 3 months, morning stiffness over 30 minutes, improvement with exercise, no improvement with rest, second-half-of-the-night pain, and alternating buttock pain suggesting bilateral sacroiliitis.

NICE NG65 axSpA referral pathway: low back pain starting before age 45 and lasting more than 3 months, plus 4 or more additional SpA features, OR 3 features plus HLA-B27 positive (commonly missed route). Additional features include onset before age 35, waking in the second half of the night, buttock pain, improvement with movement, NSAID response within 48 hours, first-degree relative with SpA, and current or past enthesitis, psoriasis, uveitis, or IBD.

ASAS classification criteria for axSpA require back pain of 3 months or more and onset under 45, plus either the imaging arm (sacroiliitis on imaging + at least 1 SpA feature) or the clinical arm (HLA-B27 positive + at least 2 SpA features). Modified New York criteria for radiographic axSpA (AS) require definite radiographic sacroiliitis (bilateral grade 2 or above, or unilateral grade 3 or above) plus clinical criteria.

Axial examination: modified Schober's test (marks 10 cm above and 5 cm below the PSIS; normal lumbar flexion increases the distance by 5 cm or more), reduced lateral flexion and cervical rotation, reduced chest expansion at the 4th intercostal space, SIJ provocation tests (compression, distraction, FABER, Gaenslen's), and, in advanced disease, loss of lumbar lordosis with increased thoracic kyphosis. Examine enthesitis sites: Achilles insertion, plantar fascia origin, tibial tuberosity, patellar tendon, iliac crest, greater trochanter.

Psoriatic arthritis - five Moll and Wright patterns:

• •Asymmetrical oligoarthritis (most common, lower-limb predominant, dactylitis characteristic).
• •Symmetrical polyarthritis (RA-like; DIP involvement and nail changes favour PsA).
• •DIP-predominant (characteristic; correlates with adjacent nail dystrophy).
• •Spondylitic (axial, often asymmetrical unlike AS).
• •Arthritis mutilans (rare, destructive osteolysis with telescoping digits and pencil-in-cup deformity).

Hallmark PsA features distinguishing it from RA: dactylitis ('sausage digit', a functional flexor sheath enthesitis), enthesitis, nail dystrophy (pitting most common, onycholysis, subungual hyperkeratosis, ridging; present in ~80% and correlates with DIP disease), DIP involvement, and asymmetry. Skin psoriasis usually precedes the arthritis but PsA can appear first - check hidden sites (scalp, navel, gluteal cleft, ears). RF and anti-CCP are typically negative.

CASPAR classification criteria for PsA: established inflammatory articular disease (joint, spine, or entheseal) plus 3 or more points from current psoriasis (2 points; personal or family history of psoriasis scores 1), nail dystrophy, negative RF, dactylitis (current or past), and juxta-articular new bone formation.

Reactive arthritis: asymmetrical lower-limb oligoarthritis 1-6 weeks after a GI (Salmonella, Shigella, Yersinia, Campylobacter) or urogenital (Chlamydia) infection. Classic triad of arthritis, urethritis, and conjunctivitis is present in a minority. Usually self-limiting in 3-6 months; around 15-20% develop chronic disease. NICE NG65 advises against routine infective antibody testing.

Enteropathic arthritis: peripheral disease (type 1 correlates with bowel activity; type 2 independent) or axial disease (independent of bowel activity).

Extra-articular features: acute anterior uveitis is the most common extra-articular feature of axSpA (~25-40% of AS - unilateral painful red eye, photophobia, episodic; same-day ophthalmology). Also psoriasis, IBD, aortic regurgitation, apical lung fibrosis, increased CV risk, and osteoporosis (vertebral bodies between syndesmophytes are osteoporotic, raising spinal fracture risk).

NICE NG65 frames investigation around clinical suspicion. The diagnosis is clinical, supported by imaging and bloods. Negative tests do not exclude SpA.

Blood tests: consider HLA-B27 testing as part of the assessment (positive in >90% of AS, ~70% of axSpA, ~60% of ReA, ~50% of enteropathic SpA, ~20% of PsA), but interpret in clinical context. CRP and ESR are normal in up to 40% of active axSpA. RF and anti-CCP are typically negative in SpA and help distinguish from RA. Baseline FBC, U&E, and LFTs are required before treatment.

SIJ imaging:

• •Plain radiographs: modified New York criteria grade sacroiliitis from 0 to 4. Grade 2 or above bilateral, or grade 3 or above unilateral, classifies as AS. Radiographic changes take years to develop; X-rays are often normal in early axSpA.
• •MRI of the SIJs is the key early-diagnosis investigation per NICE NG65 when X-rays are normal or inconclusive. Bone marrow oedema on STIR/T2 indicates active sacroiliitis. Interpret in clinical context, as similar changes can be seen with mechanical loading and postpartum change.

Spinal imaging:

Established AS X-rays show syndesmophytes (thin and marginal in AS; bulkier and asymmetrical in PsA/ReA), bamboo spine, vertebral squaring, Romanus lesions (shiny corners), and Anderson lesions. MRI spine identifies active vertebral corner inflammatory lesions.

Peripheral imaging:

• •USS detects enthesitis (thickening, hypoechogenicity, Doppler signal, erosions, enthesophytes), synovitis, dactylitis, and tenosynovitis.
• •X-rays in PsA show erosions, joint-space narrowing, DIP involvement, pencil-in-cup deformity (arthritis mutilans), periosteal new bone formation ('fluffy periostitis', a distinctive PsA feature), osteolysis, and ankylosis.

NICE NG65 anchors axSpA practice; PsA follows PsA-specific NICE technology appraisals. Treatment aims to control symptoms, suppress inflammation, prevent structural damage, and maintain function.

Axial SpA:

• •First-line: NSAIDs at the lowest effective dose with gastroprotection. Try at least 2 NSAIDs before escalating. Maximum doses may be needed. A good NSAID response within 48 hours is itself a SpA feature per NICE NG65. Any effect on radiographic progression remains uncertain.
• •Second-line: advanced therapy when 2 or more NSAIDs at maximum tolerated dose have failed and disease activity criteria are met (BASDAI of 4 or above and spinal pain VAS of 4 or above per the relevant NICE technology appraisals). For non-radiographic axSpA specifically, NICE requires objective inflammation (raised CRP OR MRI bone marrow oedema) for biologic funding - an important UK-specific point.
• •Conventional DMARDs (methotrexate, sulfasalazine, leflunomide) are NOT effective for axial disease and should not delay advanced therapy.

Advanced therapy choices for axSpA:

• •TNF-alpha inhibitors - two distinct classes with a critical distinction. Monoclonal antibodies (adalimumab, infliximab, certolizumab, golimumab) effectively treat axial disease, peripheral arthritis, enthesitis, AND associated uveitis and IBD. The soluble TNF receptor (etanercept) treats axial and peripheral SpA but does NOT effectively treat IBD and is less effective for uveitis. This distinction is regularly tested.
• •IL-17 inhibitors (secukinumab, ixekizumab) and the dual IL-17A/F inhibitor bimekizumab: effective for axial disease, peripheral arthritis, enthesitis, and skin psoriasis. May worsen IBD - avoid even in patients with a history of IBD that is currently quiescent.
• •JAK inhibitors (tofacitinib, upadacitinib): NICE-approved for axSpA in specific appraisals. MHRA caution in patients aged 65 and over, with CV disease history, malignancy history, or current/long-term smoking unless no alternatives exist.

Psoriatic arthritis: NSAIDs for mild peripheral disease. Conventional DMARDs (methotrexate first-line, especially when significant skin disease coexists) DO work for peripheral PsA, in contrast to axial SpA. For inadequate csDMARD response, advanced therapy options include TNF-alpha inhibitors, IL-17 inhibitors, the IL-12/23 inhibitor ustekinumab, IL-23 inhibitors (guselkumab, risankizumab), JAK inhibitors, and the PDE4 inhibitor apremilast.

Reactive arthritis: treat any active triggering infection (Chlamydia: doxycycline or azithromycin). Antibiotics do not modify post-infectious arthritis once the triggering infection has resolved. NSAIDs for symptoms; intra-articular corticosteroids for persistently inflamed joints; csDMARDs (sulfasalazine, methotrexate) for chronic or relapsing disease lasting beyond 6 months.

Enteropathic arthritis: treat the underlying IBD; TNF-alpha monoclonal antibodies (adalimumab, infliximab) treat bowel and joints simultaneously. Use IL-17 inhibitors with caution given the IBD risk. NSAIDs may exacerbate bowel disease. Coordinate with gastroenterology.

Cardiovascular risk: increased in SpA; annual assessment. Osteoporosis risk is increased in AS despite new bone formation; DEXA when clinically indicated. Smoking is associated with worse radiographic progression in AS, and cessation is strongly recommended.

NICE NG65 recommends an individualised exercise programme for everyone with axSpA. Spinal mobility (cervical, thoracic, and lumbar with particular focus on extension), chest expansion exercises, paraspinal and core strengthening, postural awareness, and daily ROM are the core components. Aerobic exercise and swimming are especially beneficial - low-impact and naturally encouraging spinal extension. Hydrotherapy reduces stiffness and increases range of motion. Sleep position matters: a firm mattress and one thin pillow (or none) to maintain spinal extension.

Smoking cessation improves both radiographic progression and treatment response. NASS (National Axial Spondyloarthritis Society) provides patient support and structured exercise programmes and is an important signpost. For peripheral SpA (PsA, ReA), apply load modification, progressive enthesitis loading, orthotic input, and occupational therapy for hand and foot function. Surgical options include total hip replacement for hip involvement in AS, spinal osteotomy for severe fixed kyphotic deformity (specialist centres), and spinal fracture fixation given the unstable carrot-stick/trans-discal fracture patterns of the ankylosed spine.

• •NICE NG65 (Spondyloarthritis in over 16s) - the definitive UK guideline; promotes earlier recognition, structured referral pathway, and MRI of the SIJs for early diagnosis when X-rays are inconclusive.
• •ASAS classification criteria - the modern axSpA criteria with imaging and clinical arms; underpins UK practice and biologic eligibility.
• •Modified New York criteria - define radiographic axSpA (AS); require definite radiographic sacroiliitis plus clinical features.
• •CASPAR classification criteria - the modern criteria for PsA; established inflammatory arthritis plus 3 or more points from psoriasis, nail disease, RF-negative status, dactylitis, and juxta-articular new bone.
• •NICE technology appraisals (axSpA and PsA biologics) - sequencing of TNF inhibitors, IL-17 inhibitors, IL-23 inhibitors, and JAK inhibitors. Non-radiographic axSpA requires objective inflammation for advanced therapy funding.

• •Inflammatory back pain: onset under 40, over 3 months, improves with exercise, second-half-of-night pain.
• •HLA-B27 positive in over 90% of AS but not diagnostic; negativity does not exclude SpA.
• •MRI SIJ bone-marrow oedema is the key early-diagnosis sign when X-rays are normal.
• •TNF monoclonal antibodies treat uveitis and IBD; etanercept does not.
• •IL-17 inhibitors may worsen IBD; avoid in active or quiescent IBD.
• •PsA pencil-in-cup signals arthritis mutilans; nail pitting correlates with DIP disease.