What is the diagnosis for a 61-year-old female with symmetric joint involvement, ulnar deviation, swan neck deformities, nail changes, and chronic low backache, with lab results showing low RF titer and negative anti-CCP?

Seronegative Rheumatoid Arthritis

This patient has seronegative rheumatoid arthritis (RA), characterized by symmetric polyarthritis with classic hand deformities (ulnar deviation, swan neck deformities, interosseous wasting), foot involvement (hammer toes, pes planovalgus), negative RF and anti-CCP antibodies, and low inflammatory markers. 1, 2

Key Diagnostic Features Supporting Seronegative RA

Hand and Wrist Involvement

• Bilateral ulnar deviation at MCP joints and wrists is pathognomonic for RA, distinguishing it from other inflammatory arthropathies 2, 3
• Swan neck deformities of the ring and little fingers bilaterally are classic RA deformities caused by chronic synovitis 4, 3
• Interosseous muscle wasting, dorsal hand flattening, and thenar/hypothenar wasting indicate chronic inflammatory disease with muscle atrophy 4, 3
• Symmetric involvement of small joints is characteristic of RA, not psoriatic arthritis which typically shows asymmetric distribution 1, 2

Foot Deformities

• Bilateral hindfoot valgus and pes planovalgus are common in RA due to posterior tibial tendon dysfunction from chronic inflammation 2
• Hammer toe deformities and toe crowding result from chronic synovitis affecting the metatarsophalangeal joints 2, 3
• Plantar tenderness indicates active inflammatory involvement of the foot 2

Serologic Profile

• RF 6.4 IU/mL (normal) and anti-CCP <0.5 (negative) confirm seronegative status, which occurs in approximately 20-30% of RA patients 1, 5, 6
• ESR 4 and hsCRP 0.52 are surprisingly low despite active disease, which can occur in seronegative RA 1, 7
• The absence of elevated inflammatory markers does not exclude RA, particularly in seronegative disease 1, 7

Critical Differential Diagnoses Excluded

Psoriatic Arthritis - Excluded

• No psoriatic plaques, nail pitting, or oil drop changes rule out psoriatic arthritis 8, 2
• No dactylitis or enthesitis (specifically no Achilles tendon tenderness), which are pathognomonic for PsA 8, 2
• Symmetric polyarthritis pattern favors RA over PsA, which typically shows asymmetric involvement 1, 2
• The nail dystrophy present is thickened and hyperkeratotic rather than pitting or oil drop changes, consistent with chronic mechanical trauma from deformity rather than psoriasis 8, 2
• DIP joints are not primarily involved - the deformities are at the MCP and PIP levels, not DIP 2

Axial Spondyloarthritis - Excluded

• No inflammatory back pain characteristics (the chronic low backache is likely mechanical from altered gait) 8
• No sacroiliitis symptoms 8
• HLA-B27 pending but clinical picture does not support spondyloarthritis 8

Osteoarthritis - Excluded

• Age 61 with progressive symptoms over 3-4 years suggests inflammatory rather than degenerative disease 8, 7
• Swan neck and ulnar deviation deformities are not seen in osteoarthritis 7, 2
• Symmetric small joint involvement is atypical for primary osteoarthritis 7

Diagnostic Workup Recommendations

Imaging Studies Needed

• Plain radiographs of hands, wrists, and feet should be obtained immediately to assess for erosive changes, joint space narrowing, and periarticular osteopenia characteristic of RA 8, 1
• MRI with gadolinium of hands/wrists if radiographs are negative, as MRI has superior sensitivity for detecting early erosions and bone marrow edema 1
• The presence of carpal and pericapitate abnormalities on imaging would strongly support RA over other diagnoses 8

Additional Laboratory Testing

• Complete the HLA-B27 testing to definitively exclude spondyloarthropathy, though clinical picture makes this unlikely 8
• ANA and anti-ENA panel to exclude lupus or overlap syndromes, given the seronegative status 8
• Repeat inflammatory markers during symptomatic flare if possible, as they may be more elevated during active disease 8, 1

Clinical Reasoning and Pitfalls

Why This is Seronegative RA Despite Low Inflammatory Markers

• Approximately 20-30% of RA patients are seronegative for both RF and anti-CCP 5, 6
• Low inflammatory markers can occur in established RA, particularly in patients with chronic disease and lower current activity 1, 7
• The pattern of deformities (swan neck, ulnar deviation, symmetric polyarthritis) is virtually diagnostic of RA regardless of serologic status 1, 2, 4

Common Diagnostic Pitfalls to Avoid

• Do not dismiss RA diagnosis based solely on negative serology - seronegative RA represents 20-30% of cases and can be equally destructive 1, 5, 6
• Do not confuse nail dystrophy from mechanical trauma with psoriatic nail changes - true psoriatic nails show pitting and oil drop changes, not present here 8, 2
• Do not attribute all symptoms to osteoarthritis in a 61-year-old - the symmetric small joint involvement and characteristic deformities indicate inflammatory disease 7, 2
• Low inflammatory markers do not exclude active inflammatory arthritis - clinical examination showing synovitis is more important than laboratory values 1, 7

Confirming Inflammatory vs. Mechanical Disease

• Physical examination should assess for soft tissue swelling, warmth, and true synovitis at MCP and PIP joints 7
• Ultrasonography with power Doppler can detect active synovitis even when inflammatory markers are low, and should be performed if clinical assessment is equivocal 7
• Morning stiffness duration >30 minutes would support inflammatory disease 8, 7

Management Implications

Immediate Treatment Considerations

• Early DMARD therapy is essential even in seronegative RA to prevent further joint destruction 2, 3
• Methotrexate is typically first-line therapy for RA regardless of serologic status 2
• The presence of established deformities indicates this is not early RA, suggesting previous untreated or undertreated disease 4, 3

Surgical Considerations

• Swan neck and ulnar deviation deformities may require surgical correction if they significantly impair function 4, 3
• Surgical staging depends on PIP joint flexibility and articular cartilage state - soft tissue procedures alone may be insufficient in late-stage deformities 4
• Comprehensive preoperative evaluation including cervical spine assessment is mandatory before any hand surgery in RA patients 4, 3