01OverviewDefinition, clinical context and the essential points that orientate the chapter.
Peripheral spondyloarthritis is an umbrella phenotype rather than a single cause. It includes psoriatic, reactive, enteropathic and undifferentiated disease. Build the diagnosis from distribution and associated features, not one test. Examine every joint, enthesis and digit, skin and nails, spine and eyes; record previous infection, bowel symptoms and family history.
Enthesitis should be distinguished from mechanical tendinopathy. Inflammatory features include multiple sites, morning stiffness, associated synovitis or dactylitis and spondyloarthritis context. Ultrasound can support accessible inflammation but operator and mechanical effects limit specificity. HLA-B27 modifies probability most when the phenotype is already plausible.
Baseline investigation includes FBC, renal, liver, CRP and ESR, with RF and anti-CCP when RA is an alternative. Aspirate a hot joint. Use radiography for structural disease and MRI for selected axial or deep questions. Test infection, bowel or skin disease according to clinical evidence rather than applying a uniform panel.
Treatment targets the active domain. Physiotherapy, exercise and occupational adaptation remain foundational. NSAIDs are reviewed rather than indefinite. Conventional DMARDs can treat persistent peripheral arthritis but not reliably axial disease. Specialist targeted therapy follows NICE and BSR pathways and must account for infection, pregnancy, vaccination and coexisting bowel or skin disease.
Key points
- Peripheral spondyloarthritis is recognised from asymmetric arthritis, enthesitis or dactylitis plus psoriasis, uveitis, bowel disease, recent infection, axial symptoms or family history.
- Inspect skin, scalp, nails and hidden flexures and ask about eye, bowel and genitourinary disease even when the referral says isolated tendon pain.
- HLA-B27 and inflammatory markers can support but neither confirm nor exclude peripheral disease.
- Aspirate a newly hot effusion because septic and crystal arthritis can mimic or coexist with spondyloarthritis.
- Use exercise, physiotherapy and load modification for function while avoiding prolonged immobilisation of inflammatory enthesitis.
- NSAIDs may reduce symptoms when safe; local corticosteroid injection can be considered after infection exclusion and with care around high-risk tendon sites.
- Persistent peripheral arthritis may require a conventional DMARD; refractory arthritis, enthesitis or dactylitis may need specialist targeted therapy.
- Coordinate medicine choice with psoriasis, inflammatory bowel disease and uveitis because efficacy and adverse effects differ across classes.
02AetiologyUnderlying causes, associations and risk factors, with why each one matters.
Shared spondyloarthritis susceptibility
HLA and other immune variants interact with skin, gut and genitourinary inflammation to produce a related family of peripheral phenotypes.
Entheseal mechanical interaction
Repetitive loading and microdamage at insertion sites can activate immune inflammation in a susceptible host, particularly in lower limbs.
Associated inflammatory disease
Psoriasis, inflammatory bowel disease, uveitis and preceding infection provide different contexts for otherwise similar arthritis, enthesitis and dactylitis.
03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.
- 1Enthesis organ inflammation
Inflammation involves tendon or ligament insertion, adjacent bursa, bone and synovium, producing focal pain, swelling and new bone responses.
- 2Synovial and digital inflammation
Peripheral synovitis and flexor tenosynovitis combine with soft-tissue oedema to create asymmetric arthritis and whole-digit dactylitis.
- 3Multidomain cytokine signalling
TNF, IL-17 and related pathways link joint, skin, bowel and eye disease while allowing activity to differ between organs.
04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.
Knee, ankle or foot synovitis with an uneven distribution and associated entheseal or extra-articular features supports peripheral spondyloarthritis.
Uniform whole-digit swelling reflects combined joint, tendon-sheath, entheseal and soft-tissue inflammation and carries substantial diagnostic weight.
Achilles, plantar, patellar or other insertional pain at several sites with morning stiffness and associated disease suggests inflammatory enthesitis.
Pain, photophobia, redness and blurred vision needs same-day ophthalmic assessment and should be communicated to rheumatology.
05InvestigationsWhat to request, why it matters and how to interpret it.
Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.
- 01
Domain-based clinical examinationFirst step - Why
- Document peripheral joints, entheses, dactylitis, axial signs, skin, nail, eye and bowel associations.
- Interpretation and limitations
- Tenderness without swelling is less specific; interpret insertional pain using load, distribution and associated inflammatory evidence.
- 02
FBC, renal, liver, CRP and ESR - Why
- Assess inflammation, organ status and baseline safety for anti-inflammatory or disease-modifying treatment.
- Interpretation and limitations
- Normal markers do not exclude disease; raised values also require infection, bowel activity and other sources to be considered.
- 03
RF, anti-CCP and HLA-B27 when indicated - Why
- Refine rheumatoid and spondyloarthritis probabilities after the phenotype is defined.
- Interpretation and limitations
- None is a stand-alone diagnosis. HLA-B27 performance varies by population and RF may be incidental.
- 04
Synovial-fluid analysis - Why
- Exclude infection and crystals in acute or disproportionate effusion.
- Interpretation and limitations
- Send culture and crystals together and retain infection concern despite crystal identification when systemic or host-risk features persist.
- 05
Ultrasound, radiography or MRI - Why
- Support uncertain enthesitis or synovitis, document damage or evaluate emerging axial disease.
- Interpretation and limitations
- Mechanical loading creates imaging abnormalities; use site-specific clinical concordance and do not delay referral for a normal early study.
06Differential diagnosisRealistic alternatives and the features that help distinguish them.
Rheumatoid arthritis
Symmetrical small-joint synovitis, rheumatoid serology and absence of enthesitis or dactylitis supports RA, though phenotypes can overlap.
Crystal or septic arthritis
Abrupt monoarthritis, marked warmth or systemic illness requires synovial culture and crystal analysis before a chronic inflammatory label.
Mechanical enthesopathy
Pain tightly linked to load without swelling, inflammatory features or associated disease may represent mechanical tendon insertion pathology.
Sarcoid or connective-tissue disease
Erythema nodosum, hilar disease, systemic rash, Raynaud phenomenon, renal findings or cytopenia broadens the inflammatory differential.
Additional chapter-specific clues
One severely painful hot restricted joint, particularly during immunosuppression, needs urgent aspiration and culture.
07ManagementImmediate care, first-line treatment, alternatives and escalation.
01New peripheral phenotypeName the domains and associated diseaseFirst stepPersistent asymmetric arthritis, dactylitis or multisite enthesitis lacks an acute infection signal.+
- 1Map joints, entheses, digits, spine, skin, nails and eye or bowel history and obtain baseline treatment-safety tests.
- 2Refer to rheumatology through the peripheral spondyloarthritis pathway, highlighting psoriasis, uveitis, IBD, infection and family history.
- 3Begin safe symptom and functional care while preserving diagnostic visibility and arranging urgent review for one hot joint or eye symptoms.
02Persistent active diseaseEscalate by dominant domainEscalationPeripheral arthritis, enthesitis or dactylitis remains active despite appropriate initial care.+
- 1Confirm objective inflammation and separate structural tendon disease, obesity-related load, infection and pain amplification.
- 2Use a conventional DMARD for persistent peripheral arthritis where appropriate, and assess refractory disease for specialist targeted therapy.
- 3Choose treatment with dermatology or gastroenterology when skin or bowel disease is active and monitor each domain separately.
03Axial symptoms emergeReclassify and use the axial pathwayInflammatory back pain, buttock pain or spinal restriction develops during peripheral follow-up.+
- 1Reassess axial features, neurological red flags and family history and examine spinal movement and hips.
- 2Use the NICE axial referral and sacroiliac radiography-to-MRI sequence; normal HLA-B27 or CRP does not end assessment.
- 3Adjust treatment because conventional peripheral DMARDs do not reliably control axial inflammation.
Key medicines and prescribing safety2 treatments · regimens, roles and cautions+
Naproxen
Common adult dosing is 250–500 mg orally twice daily with food for a reviewed trial when risk permits.Review ulcer, renal, cardiovascular, anticoagulant and bowel risks and use the lowest effective dose with gastroprotection when indicated. From 20 weeks of pregnancy, avoid systemic NSAIDs unless necessary and then keep exposure minimal; after 28 weeks naproxen is contraindicated.
Sulfasalazine
Commonly started at 500 mg once daily and increased gradually toward 1 g twice daily under specialist monitoring.Monitor FBC, renal and liver function; counsel about serious rash, gastrointestinal intolerance, blood dyscrasia and reversible oligospermia, and review sulfonamide allergy and azathioprine or 6-mercaptopurine interaction. Pause it for a serious infection until recovery and specialist review. In pregnancy, give folic acid 5 mg daily during periconception and the first trimester.
08ComplicationsImportant consequences, why they occur and why they matter clinically.
Erosive peripheral arthritis
Persistent synovitis can damage cartilage and bone, deform joints and reduce work and mobility before axial symptoms ever appear.
Chronic enthesitis and dactylitis
Ongoing insertional and whole-digit inflammation causes persistent pain, tendon dysfunction, impaired gait and treatment-resistant functional disability.
Axial evolution
Some patients develop sacroiliac and spinal disease over time, requiring reassessment when inflammatory back pain or restricted movement appears.
Extra-articular organ harm
Uveitis, psoriasis and bowel disease may dominate morbidity and determine the urgency and safe choice of targeted therapy.
09Monitoring and follow-upTreatment response, safety checks and longer-term review.
- Record swollen joints, dactylitis, entheseal sites, axial symptoms, function and extra-articular activity.
- Monitor laboratory safety at regimen-specific intervals and after conventional DMARD dose changes.
- Ask about eye pain, bowel activity, skin change, infection and pregnancy at every treatment review.
- Review NSAID blood pressure, renal, gastrointestinal and cardiovascular safety.
- Reassess the diagnosis if objective inflammation remains absent or symptoms become widespread and non-anatomical.
10Special situationsVariants, exceptions and circumstances that change the usual approach.
Peripheral SpA is a phenotype
The label organises recognition while psoriasis, bowel disease, infection or an evolving axial pattern may later refine the diagnosis.
Enthesitis needs context
Single-site insertional pain is common mechanically; multisite disease, stiffness and associated features increase inflammatory probability.
Dactylitis crosses structures
Whole-digit disease reflects more than one joint and is easily underestimated by standard swollen-joint counts.
HLA is supportive
A positive result changes probability within a compatible phenotype but cannot explain symptoms by itself.
Treatment follows the domain
Peripheral synovitis, enthesitis, axial disease, psoriasis and IBD respond differently, so one ladder does not fit every patient.
11Common pitfallsFrequent interpretation and management errors.
- 01
Calling isolated mechanical heel pain inflammatory from HLA-B27 positivity.
- 02
Missing hidden psoriasis, nail disease or bowel symptoms.
- 03
Using a conventional DMARD as sole treatment for persistent axial inflammation.
- 04
Injecting an acutely hot site before infection is excluded.
- 05
Measuring only joints and ignoring dactylitis, enthesitis and function.