What is the most likely diagnosis for a diabetic patient with a 6-month history of bilateral pain in the proximal interphalangeal (PIP) and metacarpophalangeal (MCP) joints, dry eyes, elevated erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP), and negative Anti-SSA (Anti-Sjögren's syndrome antigen A)?

Rheumatoid Arthritis

The most likely diagnosis is Rheumatoid Arthritis (RA). This patient presents with the classic triad of bilateral symmetric small joint involvement (PIP and MCP joints), elevated inflammatory markers (ESR and CRP), and 6-month symptom duration—all meeting the core diagnostic criteria for RA despite negative Anti-SSA antibodies.1

Diagnostic Reasoning

This clinical presentation scores highly on the 2010 ACR/EULAR Classification Criteria for RA:

• Joint involvement (4-10 small joints) = 3 points - The bilateral PIP and MCP involvement represents classic small joint distribution for RA 1, 2
• Abnormal acute phase reactants (elevated ESR and CRP) = 1 point 1
• Duration ≥6 months = 1 point 1
• Total = 5 points minimum (serology unknown, but ≥6/10 confirms definite RA) 1

The symmetric involvement of MCPs and PIPs is pathognomonic for RA, as these are the characteristic target joints, while DIP joints are typically spared—distinguishing it from osteoarthritis.1, 2 The 6-month duration with persistent symptoms indicates established disease rather than transient inflammatory arthritis.1

Markedly elevated inflammatory markers (high ESR and CRP) strongly support active inflammatory arthritis and predict aggressive disease with high risk of radiographic progression if untreated.1, 3 This level of systemic inflammation far exceeds what would be expected in non-inflammatory conditions.1

Why Not the Other Options?

Sjögren syndrome (Option B) is effectively ruled out by the negative Anti-SSA antibodies. While dry eyes are present, Anti-SSA is positive in 40-60% of primary Sjögren's cases, and the prominent inflammatory polyarthritis with markedly elevated CRP/ESR is far more consistent with RA with secondary sicca features rather than primary Sjögren's.1 Approximately 15-30% of RA patients develop dry eye symptoms, particularly those with secondary Sjögren's syndrome.1 The arthritis pattern and inflammatory markers dominate the clinical picture here.4

Diabetic cheiroarthropathy (Option C) is excluded because it presents as a non-inflammatory condition with painless limitation of joint mobility and skin thickening affecting joint capsules and periarticular tissues—not painful inflammatory arthritis with elevated inflammatory markers.1, 5 Diabetic cheiroarthropathy lacks the synovitis, elevated acute phase reactants, and bilateral symmetric small joint pain characteristic of this case.5

Osteoarthritis (Option D) is incompatible with this presentation. OA typically targets DIP joints (Heberden nodes) and first CMC joints while sparing MCPs, presents without significant morning stiffness, and shows normal inflammatory markers (normal CRP).6 The bilateral PIP and MCP involvement with elevated ESR/CRP indicates inflammatory rather than degenerative disease.1, 6

Critical Next Steps

Immediate serologic testing is essential:

• Rheumatoid factor (RF) and anti-citrullinated protein antibodies (ACPA) should be ordered immediately, as these are highly predictive of RA diagnosis and prognosis 1, 3
• Complete blood count with differential to assess for cytopenias before starting treatment 1
• Comprehensive metabolic panel including liver and renal function 1

Baseline imaging is mandatory:

• Bilateral hand, wrist, and foot X-rays to assess for erosions, which predict RA diagnosis and disease persistence 1, 3
• Presence of erosions on baseline radiographs is highly predictive for aggressive disease 1

Treatment should not be delayed waiting for complete serologic workup. Seronegative RA accounts for 20-30% of cases, and negative RF does not exclude RA diagnosis.1 The clinical presentation with definite synovitis in multiple small joints takes precedence over serologic findings.1

Start methotrexate 15 mg weekly immediately as first-line DMARD, with plan to escalate to 20-25 mg weekly, and consider short-term low-dose prednisone (10-20 mg daily) as bridge therapy while awaiting DMARD effect.1 Early treatment prevents irreversible joint damage.1

Common Pitfalls to Avoid

Do not dismiss RA diagnosis based on negative Anti-SSA alone—this antibody is specific for Sjögren syndrome, not RA. The absence of Anti-SSA does not exclude RA; it simply makes primary Sjögren's unlikely.4

Do not delay treatment waiting for positive RF or ACPA—seronegative RA is common and has similar prognosis to seropositive disease.1 Clinical synovitis with elevated inflammatory markers for 6 months warrants immediate DMARD therapy.1

Do not confuse diabetic hand complications with inflammatory arthritis—diabetic cheiroarthropathy is painless and non-inflammatory, while this patient has painful joints with systemic inflammation.5