Differentiating Types of Arthritis

Initial Assessment and Diagnosis

The American College of Rheumatology recommends a systematic clinical assessment focusing on six key factors: disease chronology, presence of inflammation, joint distribution pattern, extra-articular manifestations, disease course, and patient demographics to guide diagnosis 1, 2
Inflammatory arthritis presents with prolonged morning stiffness, palpable synovitis, and improvement with activity, according to the European League Against Rheumatism 1, 2
Non-inflammatory arthritis, such as osteoarthritis, shows brief morning stiffness, bony hypertrophy, and worsening with activity 1, 2
The American College of Rheumatology and European League Against Rheumatism suggest that a score of ≥6/10 points using the 2010 ACR/EULAR Classification Criteria for RA indicates definite RA classification 3, 4

The American College of Rheumatology recommends ESR and CRP tests at baseline for diagnostic and prognostic purposes, but normal values do not exclude inflammatory arthritis 1, 5, 3
RF and/or ACPA testing is predictive of RA diagnosis and prognosis, with RF having 70% specificity and 60% sensitivity, and ACPA having 90% specificity and 60% sensitivity, according to the American College of Rheumatology 1, 5, 3
Complete blood count with differential, comprehensive metabolic panel, and urinalysis are also recommended as part of the standard workup 3

The American College of Rheumatology recommends plain radiographs of affected joints at baseline, with bilateral hand, wrist, and foot X-rays for RA evaluation 1, 5, 2
Ultrasound is superior to clinical examination for detecting synovitis and structural damage, while MRI with IV contrast is more sensitive than ultrasound in early stages, according to the European League Against Rheumatism 3
The American College of Rheumatology suggests that a 28-joint count examination assessing PIPs, MCPs, wrists, elbows, shoulders, and knees for tenderness and swelling should be performed 3

Disease duration ≥6 weeks, involvement of small joints and/or knee, and ACPA and/or RF positivity predict chronicity, according to the American College of Rheumatology 3, 5
Presence of radiographic erosion also predicts chronicity, according to the European League Against Rheumatism 2

The 2010 ACR/EULAR Classification Criteria for RA uses a scoring system with points for joint involvement, serology, acute phase reactants, and duration of symptoms, with a score of ≥6/10 points indicating definite RA classification 3, 4
The criteria include:

Symmetric involvement of small hand or foot joints strongly indicates rheumatoid arthritis, particularly in women around 30 years old. 6
Asymmetric, pauci‑articular involvement of large weight‑bearing joints (knees, ankles, hips) points toward reactive arthritis or peripheral seronegative spondyloarthropathy. 7
Conjunctivitis, urethritis, or a recent gastrointestinal/genitourinary infection suggests reactive arthritis. 8
Inflammatory back pain or enthesitis raises suspicion for axial spondyloarthropathy (including ankylosing spondylitis). 7
Dry‑eye and dry‑mouth symptoms may indicate Sjögren’s syndrome or an overlap connective‑tissue disorder. 8

Female gender and an age of approximately 30 years increase the likelihood of rheumatoid arthritis and systemic lupus erythematosus. 6

ANA testing with reflex to extractable nuclear antigens is recommended in young women with systemic features to assess for systemic lupus erythematosus. 6
HLA‑B27 testing should be performed when clinical features (inflammatory back pain, enthesitis, recent infection, or family history) suggest a seronegative spondyloarthropathy. 7, 6
Baseline complete blood count, comprehensive metabolic panel (including uric acid), and urinalysis are useful to detect anemia of chronic disease, gout, renal involvement, or lupus‑related urinary abnormalities. 6

A chest radiograph is advised to exclude sarcoidosis or tuberculosis in patients presenting with systemic symptoms. 6

Disease duration of ≥ 6 weeks, involvement of small joints and/or knees, positive anti‑citrullinated protein antibody (ACPA) or rheumatoid factor (RF), and radiographic erosions predict a chronic course that warrants early disease‑modifying therapy. 6