What is the diagnosis and management for a patient with rheumatoid arthritis (RA) presenting with a red nodule on the lateral aspect of the thumb's interphalangeal (IP) joint?

Diagnosis: Rheumatoid Nodule

This red nodule on the lateral thumb IP joint in a patient with established rheumatoid arthritis is most likely a rheumatoid nodule, which is the most common extra-articular manifestation of RA, occurring in approximately 25% of seropositive patients. 1, 2

Diagnostic Reasoning

Why This is a Rheumatoid Nodule

• Rheumatoid nodules are the most common extra-articular lesion in RA, present in about 25% of seropositive patients with severe disease 1, 2
• These nodules characteristically occur over pressure points and extensor surfaces, making the lateral aspect of the thumb IP joint a typical location 3
• The presence of erythema (red appearance) suggests either active inflammation within the nodule or possible complications such as local irritation, trauma, or early infection 1

Critical Differential Considerations

While rheumatoid nodule is most likely, you must exclude:

• Gout superimposed on pre-existing RA - can present as red nodular lesions and may coexist with RA, particularly at sites of previous joint damage 4
• Psoriatic arthritis - can target DIP joints (though this is the thumb IP, not a typical DIP) and may show asymmetric involvement 4, 5
• Infection - any red, warm nodule in an immunosuppressed RA patient warrants consideration of septic arthritis or soft tissue infection 6
• Accelerated rheumatoid nodulosis - particularly if the patient is on methotrexate, anti-TNF biologics, or leflunomide, which paradoxically can increase nodule development 2, 3

Immediate Assessment Steps

Clinical Examination Details to Document

• Palpate for firmness versus fluctuance - rheumatoid nodules are typically firm and non-tender, while infection would be fluctuant and tender 1
• Assess for warmth and tenderness - significant warmth or tenderness raises concern for infection or acute inflammation requiring urgent intervention 1
• Check for skin breakdown or ulceration - erosion through skin increases infection risk and may require surgical intervention 1
• Examine for nerve compression symptoms - numbness or tingling suggests compression requiring surgical evaluation 1
• Document size and mobility - fixed nodules may indicate deeper involvement 3

Laboratory and Imaging Workup

• If infection is suspected (warmth, tenderness, systemic symptoms): obtain CBC, ESR, CRP, and consider aspiration for culture before antibiotics 6
• Confirm RF and anti-CCP status if not previously documented - rheumatoid nodules are strongly associated with seropositive disease 2, 3
• Plain radiograph of the thumb - to assess for underlying joint erosion or bone involvement that may complicate management 1
• Ultrasound can differentiate solid nodule from fluid collection if clinical examination is equivocal 4

Management Algorithm

Conservative Management (First-Line for Most Nodules)

Observation alone is appropriate for asymptomatic nodules without complications 1, 3

• No evidence supports that systemic RA therapy effectively treats existing rheumatoid nodules 3
• Paradoxically, methotrexate and TNF inhibitors can worsen nodulosis - if nodules are proliferating rapidly, discuss with rheumatology about adjusting DMARDs 2, 3
• Optimize underlying RA control - while this won't shrink existing nodules, it may prevent new ones 6

Indications for Surgical Excision

Surgical excision is indicated when nodules cause: 1

• Local pain interfering with function
• Nerve compression with neurologic symptoms
• Limited range of motion in the thumb IP joint
• Skin erosion or ulceration
• Confirmed or suspected infection
• Mechanical interference with daily activities

Surgical excision is effective with good outcomes in appropriately selected patients 1

Critical Pitfall: Methotrexate-Induced Accelerated Nodulosis

• If this patient is on methotrexate and experiencing rapid development of multiple new nodules (especially on hands), this represents accelerated rheumatoid nodulosis 2, 3
• Consider switching from methotrexate to alternative DMARD (leflunomide, sulfasalazine, or biologic) in consultation with rheumatology 2
• However, leflunomide and anti-TNF agents can also cause nodulosis, so careful drug selection is needed 2, 3

Key Clinical Pitfalls to Avoid

• Do not assume all nodules in RA patients are benign rheumatoid nodules - always exclude infection, especially if erythematous or tender 1
• Do not biopsy routinely - diagnosis is typically clinical, and biopsy is reserved for atypical presentations or when malignancy/infection cannot be excluded 2, 3
• Do not expect systemic RA therapy to resolve nodules - this is a common misconception; nodules often persist despite good disease control 3
• Do not overlook functional impairment - even "small" nodules on the thumb can significantly impair pinch grip and warrant intervention 1

When to Refer

• Urgent rheumatology consultation if: signs of infection, rapid nodule proliferation suggesting accelerated nodulosis, or need to adjust DMARD therapy 2, 3
• Orthopedic hand surgery referral if: nodule causes mechanical dysfunction, nerve compression, skin erosion, or patient desires excision for symptomatic relief 1