What is the appropriate diagnosis and treatment for a patient presenting with joint pain, swelling, and stiffness, along with laboratory findings of hyperthyroidism, folate deficiency, and significantly elevated vitamin B12 levels?

Diagnostic Approach to Joint Pain with Laboratory Abnormalities

Most Likely Diagnosis: Inflammatory Arthritis (Probable Rheumatoid Arthritis)

This patient requires urgent rheumatology referral within 6 weeks and immediate initiation of diagnostic workup for inflammatory arthritis, most likely rheumatoid arthritis (RA), given the classic triad of joint pain, swelling, and stiffness. 1, 2

Critical Initial Assessment

Joint Examination Priorities

• Perform a 28-joint count assessment examining metacarpophalangeal (MCP) joints, proximal interphalangeal (PIP) joints, wrists, elbows, shoulders, and knees for both tenderness and swelling 2, 3
• Document morning stiffness duration - stiffness lasting >60 minutes strongly suggests inflammatory arthritis rather than osteoarthritis 3, 4
• Perform squeeze test of MCPs and metatarsophalangeal (MTP) joints to assess for clinical synovitis 3
• Look for symmetric joint involvement, which is the hallmark of RA 4, 5

Essential Laboratory Testing

Immediate Priority Tests:

• Rheumatoid factor (RF) - essential for diagnosis and prognosis 2
• Anti-cyclic citrullinated peptide (anti-CCP) antibodies - highest specificity (90%) for RA 2, 3
• C-reactive protein (CRP) - preferred over ESR as it is more reliable and not age-dependent 2, 3
• Complete blood count with differential - assess for cytopenias before starting treatment 2, 3
• Comprehensive metabolic panel - baseline liver and renal function 2, 3

Secondary Tests to Consider:

• Antinuclear antibodies (ANA) if diagnosis remains uncertain to screen for other connective tissue diseases 2, 3
• HLA-B27 only if spondyloarthropathy is suspected based on axial symptoms 1, 2

Interpretation of Current Laboratory Values

Thyroid Level (112 - Likely TSH in mIU/L)

If this represents TSH of 112 mIU/L, this indicates severe hypothyroidism, not hyperthyroidism. Hypothyroidism can cause:

• Joint pain and stiffness mimicking inflammatory arthritis 6, 7
• Elevated CRP due to metabolic effects
• However, hypothyroidism alone does not cause true joint swelling - the presence of swelling indicates genuine inflammatory arthritis requiring treatment 1, 2

Folate Level (3.3 ng/mL)

• This is low-normal to borderline deficient (normal range typically 3-17 ng/mL) 1
• Folate deficiency should be corrected before starting methotrexate, as MTX further depletes folate 1
• Start folic acid 1 mg daily immediately 1

Vitamin B12 Level (1904 pg/mL)

• This is markedly elevated (normal range 200-900 pg/mL) 1, 6
• Elevated B12 is not concerning and does not require treatment 1
• This elevation may be related to supplementation or metabolic factors 6, 7

Imaging Studies Required

Baseline imaging within 1 week:

• Bilateral hand, wrist, and foot X-rays - essential for detecting erosions which predict RA diagnosis and disease persistence 1, 2, 3
• Consider ultrasound with Power Doppler if clinical examination is inconclusive, as it is superior to clinical examination for detecting subclinical synovitis 2, 3, 4

Diagnostic Scoring (2010 ACR/EULAR Criteria)

Calculate the diagnostic score (≥6/10 points needed for definite RA): 2, 3

• Joint involvement: 1-3 small joints = 2 points; 4-10 small joints = 3 points; >10 joints = 5 points
• Serology: Negative RF and ACPA = 0 points; low positive = 2 points; high positive = 3 points
• Acute phase reactants: Normal CRP/ESR = 0 points; abnormal = 1 point
• Duration: <6 weeks = 0 points; ≥6 weeks = 1 point

Critical Management Steps

Immediate Actions (Within 1 Week)

1. Correct thyroid dysfunction - start levothyroxine for severe hypothyroidism
2. Start folic acid 1 mg daily to prepare for potential methotrexate therapy 1
3. Obtain baseline imaging (hand, wrist, foot X-rays bilaterally) 2, 3
4. Complete autoimmune serology panel (RF, anti-CCP, CRP) 2, 3

If RA Confirmed (Score ≥6/10)

Start methotrexate 15 mg weekly within 3 months of symptom onset as the anchor drug, unless contraindicated 1, 2, 3

• Add folic acid 1 mg daily (already started) 1
• Consider short-term prednisone 10-20 mg daily as bridge therapy while awaiting DMARD effect 1
• Target: remission (SDAI ≤3.3) or low disease activity (SDAI ≤11) 2, 3

Monitoring Plan

• Reassess disease activity every 4-6 weeks using SDAI or CDAI 2, 3
• Repeat inflammatory markers (CRP) at each visit 2, 3
• Repeat X-rays at 6 and 12 months to monitor radiographic progression 3

Critical Pitfalls to Avoid

• Do not delay treatment waiting for positive serology - seronegative RA accounts for 20-30% of cases and has similar prognosis 3
• Do not dismiss RA diagnosis based on normal CRP/ESR - acute phase reactants can be normal even in active disease 2, 3
• Do not attribute all symptoms to hypothyroidism - true joint swelling indicates inflammatory arthritis requiring DMARD therapy 1, 2
• Do not start methotrexate before correcting folate deficiency and ensuring adequate thyroid function 1