What is the likely diagnosis and management plan for a 61-year-old female with progressive foot pain, plantar pain, and bilateral ankle and toe deformities, with a slightly elevated ESR and normal renal function?

Likely Diagnosis: Seronegative Inflammatory Arthritis (Probable Psoriatic Arthritis or Seronegative Rheumatoid Arthritis)

This patient most likely has an inflammatory arthropathy, with psoriatic arthritis being the leading differential diagnosis given the bilateral ankle valgus deformity, hammer toes, flat feet, finger deformities, and hyperkeratosis—all in the absence of classic psoriatic skin findings. 1

Diagnostic Reasoning

Clinical Features Strongly Suggesting Inflammatory Arthritis

• Progressive symmetric polyarticular involvement affecting small joints of hands and feet over 3-4 years is the hallmark presentation of inflammatory arthritis 1
• Multiple joint deformities (bilateral ankle valgus, toe varus, hammer toes, finger deformities) indicate chronic progressive disease with structural damage 2, 3
• Elevated ESR (17) with normal CRP (0.52) suggests mild systemic inflammation, though ESR has diagnostic value for inflammatory arthritis even when modestly elevated 1
• Female gender and age 61 are predictive factors for rheumatoid arthritis, though the distribution pattern here is atypical 1

Why Psoriatic Arthritis is Most Likely

• Distal joint involvement (2nd toe deformities bilaterally) is characteristic of psoriatic arthritis, as it commonly affects distal interphalangeal joints unlike rheumatoid arthritis which rarely involves these joints 1, 4
• Hyperkeratosis of the nail (right 2nd toe) may represent early nail changes of psoriasis, even without classic pitting or oil drop changes 1
• Asymmetric features (hyperkeratosis only on right side) can occur in psoriatic arthritis, which often has asymmetric presentation initially 1
• Absence of rheumatoid nodules makes seronegative RA less likely, though not excluded 1
• Up to 15% of psoriatic arthritis patients have minimal or no skin disease at presentation 1

Alternative Considerations

• Seronegative rheumatoid arthritis remains possible given symmetric small joint involvement, though the distal joint involvement is atypical 2, 3, 4
• Adult-onset Still's disease is unlikely given absence of fever, rash, sore throat, and markedly elevated inflammatory markers 1
• Peripheral arterial disease is excluded by normal pulses, no ischemic changes, and absence of vascular risk factors 1

Critical Pending Laboratory Tests

The RF, anti-CCP, and HLA-B27 results are essential for definitive diagnosis:

• If RF and anti-CCP are positive: Diagnosis is rheumatoid arthritis with high specificity 1, 2, 3
• If RF and anti-CCP are negative: Seronegative inflammatory arthritis (psoriatic arthritis or seronegative RA) 1
• If HLA-B27 is positive: Consider spondyloarthropathy spectrum, though axial symptoms are absent 1

Immediate Management Plan

Diagnostic Workup to Complete NOW

• Bilateral hand and feet radiographs to assess for erosive changes, joint space narrowing, and characteristic patterns (pericapitate narrowing suggests RA; pencil-in-cup deformities suggest psoriatic arthritis) 1, 2
• Thorough skin and nail examination by dermatology to identify subtle psoriatic changes in scalp, umbilicus, gluteal cleft, and all nails 1
• Repeat inflammatory markers (ESR, CRP) as baseline for monitoring disease activity 1
• Consider ultrasound of hands and feet to detect synovial thickening and early erosions not visible on plain films 4

Initial Symptomatic Treatment (While Awaiting Serology)

• NSAIDs (e.g., naproxen 500mg twice daily or ibuprofen 600mg three times daily) for pain and inflammation 5, 6, 7
• Activity modification without complete immobilization to prevent deconditioning 6, 7
• Proper footwear with adequate arch support and cushioning for plantar pain 5, 6
• Orthotic devices including heel cushions and arch supports for foot pain 5, 6
• Stretching exercises for plantar fascia and Achilles tendon (3-5 times daily) 5, 6, 7

Definitive Treatment Based on Serology Results

If inflammatory arthritis is confirmed (regardless of serology):

• Immediate rheumatology referral for disease-modifying antirheumatic drug (DMARD) initiation, as early treatment (within 3-6 months) prevents irreversible joint damage 2, 3
• Methotrexate is first-line DMARD for both rheumatoid arthritis and psoriatic arthritis (typically 15-25mg weekly with folic acid 1mg daily) 1, 2, 3
• TNF-alpha inhibitors (adalimumab, etanercept, or infliximab) should be added if inadequate response to methotrexate after 3 months 1, 2, 3
• Screen for hepatitis B, hepatitis C, and tuberculosis before starting biologic agents 2, 3

Common Pitfalls to Avoid

• Do not delay DMARD therapy waiting for "definitive" diagnosis—early aggressive treatment within 3-6 months is critical to prevent irreversible erosive damage 2, 3
• Do not dismiss inflammatory arthritis because inflammatory markers are only mildly elevated—clinical features trump laboratory values 1
• Do not assume absence of skin lesions excludes psoriatic arthritis—up to 15% have arthritis-predominant disease with minimal skin involvement 1
• Avoid corticosteroid injections near the Achilles tendon due to rupture risk 5, 6, 7
• Do not attribute all symptoms to mechanical/degenerative disease in a 61-year-old—the progressive nature and bilateral symmetry indicate systemic inflammatory process 1, 2

Prognosis and Monitoring

• Without treatment, 50% of inflammatory arthritis patients develop progressive joint damage within 2 years 1
• Goal of therapy is disease remission or lowest possible disease activity to prevent disability 2, 3
• Monitor disease activity with joint counts, patient-reported outcomes, and inflammatory markers every 3 months initially 2, 3
• Some patients achieve long-term remission and can taper medications after sustained disease control 2