SERONEGATIVE SPONDYLOARTHROPATHIES

Seronegative spondyloarthropathies definition

RF‑negative, HLA‑B27–associated inflammatory arthritides affecting axial and/or peripheral skeleton.

Main seronegative conditions

Ankylosing spondylitis, psoriatic arthritis, reactive arthritis, enteropathic arthritis.

HLA‑B27 significance

Strong genetic association with AS, ReA, PsA, and IBD‑related arthritis.

Common features of seronegative SpA

Sacroiliitis, enthesopathy, syndesmophytes, peripheral arthritis, uveitis.

Axial vs peripheral SpA

Axial = spine/SI joints; Peripheral = extremities (DIP, knees, ankles).

AS alternate names

Marie‑Strümpell disease, Bechterew disease.

AS definition

Chronic inflammatory disease primarily affecting axial skeleton with progressive ankylosis.

AS demographics

Young adult males; onset 15–35 years.

AS hallmark symptom

Chronic low back pain and stiffness improving with activity.

AS classic joint involvement

Sacroiliac joints (100% eventually).

AS HLA‑B27 positivity

~90%.

AS chest expansion finding

Reduced chest expansion (<2.5 cm).

AS extra‑articular features

Iritis, conjunctivitis, aortic insufficiency, pulmonary fibrosis.

AS serology

HLA‑B27 positive, ESR elevated, RF negative, ANA negative.

AS management

NSAIDs, rheumatology referral, posture preservation.

AS SI joint hallmark

Bilateral, symmetrical sacroiliitis.

AS SI joint early finding

Hazy loss of subchondral cortical definition.

AS SI joint erosions

Begin on iliac side.

AS SI joint pseudo‑widening

Seen in grade III sacroiliitis.

AS SI joint ankylosis

Occurs in ~50% of patients.

AS SI grading scale

0 normal, I suspicious, II sclerosis/erosions, III severe erosions/pseudo‑dilation, IV ankylosis.

Romanus lesion

Corner erosion at vertebral body.

Shiny corner sign

Reactive sclerosis at vertebral corners.

Vertebral squaring

Loss of anterior concavity.

Syndesmophytes in AS

Thin, marginal, vertical; create bamboo spine.

Dagger sign

Interspinous ligament ossification.

Railroad track sign

Bilateral facet capsule ossification.

Trolley track sign

Dagger sign + railroad tracks.

Whiskering

Enthesopathy at ischial tuberosities.

Andersson lesion

Inflammatory spondylodiscitis with endplate destruction.

Carrot stick fracture

Transverse fracture through ankylosed spine.

Osteitis condensans ilii

Sclerosis of inferior ilium, postpartum females, no erosions.

OA vs AS SI joints

OA has sclerosis and narrowing but no erosions or ankylosis.

Enteropathic arthritis definition

Arthritis associated with inflammatory bowel disease or GI infections.

IBD types associated

Ulcerative colitis and Crohn disease.

Enteropathic axial pattern

Similar to AS; independent of GI symptoms.

Enteropathic peripheral pattern

Non‑erosive, non‑deforming; may precede GI symptoms.

Enteropathic arthritis enthesitis

Achilles tendon, plantar fascia, tibial tuberosity, patella.

Reactive arthritis association

HLA‑B27 positive in ~80%.

Reactive arthritis triggers

Shigella, Salmonella, Yersinia, Campylobacter, C. difficile, parasites.

PsA definition

Chronic inflammatory arthritis associated with psoriasis.

PsA prevalence

Occurs in ~30% of psoriasis patients.

PsA risk factors

Nail pitting, scalp psoriasis, inverse psoriasis, family history.

PsA onset

Psoriasis precedes arthritis in 60–80% of cases.

PsA M:F ratio

1:1.

PsA systemic risks

Hypertension, obesity, diabetes, cardiovascular disease.

PsA joint distribution

Asymmetric; often DIP joints.

Dactylitis

Sausage digit.

Mouse‑ear erosions

Peripheral erosions with periostitis.

Pencil‑in‑cup deformity

Central erosions with bone resorption.

Acro‑osteolysis

Possible in PsA.

Ray pattern

All joints of one digit involved.

Bone density in PsA

Normal (unlike RA).

PsA syndesmophytes

Thick, bulky, asymmetric, non‑marginal.

PsA SI involvement

Unilateral or bilateral, asymmetric erosions/sclerosis.

PsA vs AS spine

PsA has bulkier, asymmetric syndesmophytes.

Reactive arthritis definition

Arthritis following GI or GU infection.

Classic triad

Arthritis, conjunctivitis, urethritis.

ReA HLA‑B27 association

Strong (80%).

ReA joint pattern

Asymmetric oligoarthritis, lower extremity predominant.

ReA enthesitis

Achilles tendon, plantar fascia.

ReA SI involvement

Unilateral or bilateral, asymmetric.

AS hallmark features

Bilateral SI erosions, thin marginal syndesmophytes, shiny corners, bamboo spine.

PsA hallmark features

DIP involvement, mouse ears, pencil‑in‑cup, asymmetric bulky syndesmophytes.

ReA hallmark features

Asymmetric lower extremity arthritis, enthesitis, post‑infection.

Enteropathic hallmark features

AS‑like axial disease + GI pathology.