In an older adult woman with degenerative osteoarthritis of a distal interphalangeal joint, what is the most likely cause of a soft‑tissue swelling or palpable mass and how should it be evaluated and managed?

Soft Tissue Swelling in Distal Interphalangeal Joint Osteoarthritis

Most Likely Diagnosis

The soft-tissue swelling or palpable mass in an older adult woman with degenerative osteoarthritis of the distal interphalangeal (DIP) joint most likely represents a Heberden's node, which is a posterolateral firm or hard bony enlargement characteristic of hand osteoarthritis. 1

Clinical Features of Heberden's Nodes

• Heberden's nodes are clinically defined as posterolateral firm/hard swellings at the DIP joint that represent bony osteophytes and periarticular changes associated with underlying osteoarthritis. 1
• These nodes can occur with or without radiological abnormalities and are a hallmark of nodal osteoarthritis. 1
• The presence of Heberden's nodes alone gives a 20% probability of hand OA, but this increases to 88% when the patient is over 40 years old, has a family history of nodes, and demonstrates joint space narrowing on radiographs. 1
• Women over age 40 have dramatically increased incidence of hand OA compared to men, making this demographic particularly susceptible. 1

Alternative Diagnoses to Consider

While Heberden's nodes are most common, other causes of soft-tissue swelling at the DIP joint include:

• Mucous cysts (ganglion cysts) - These are fluid-filled lesions that can occur at the DIP joint, though they are covered in separate ACR guidelines for soft tissue masses. 1
• Inflammatory arthritis - Though less likely in isolated DIP involvement, erosive osteoarthritis is a subset defined by subchondral erosion and cortical destruction. 1
• Soft tissue infection or abscess - Should be considered if there is warmth, erythema, or systemic signs. 1

Evaluation Algorithm

Step 1: Initial Clinical Assessment

• Examine for posterolateral firm/hard swellings characteristic of Heberden's nodes, assessing bilateral hands for symmetry and involvement of other joints. 1
• Document patient age (risk increases dramatically after age 40), sex (female predominance), family history of nodes, and occupational history (repetitive hand tasks increase risk). 1
• Assess for signs of infection including warmth, erythema, fluctuance, or systemic symptoms that would suggest alternative diagnoses. 1

Step 2: Initial Imaging

Plain radiographs of the hand are the fundamental first imaging study and should always be obtained. 1, 2

Radiographs can reveal:

• Joint space narrowing in DIP joints (present in 88% probability of hand OA when combined with clinical nodes and age >40). 1
• Osteophytes at the DIP joint margins. 1, 3
• Soft tissue swelling (visible in many cases). 1
• Calcification (present in 27% of soft tissue masses). 1, 2
• Bone involvement or erosions (present in 22% of cases, may indicate erosive OA subset). 1, 2

Important caveat: Radiographs may be unrewarding for small, non-mineralized, or early lesions, but they remain the essential starting point. 1, 2

Step 3: Advanced Imaging (If Indicated)

Ultrasound is the preferred next imaging modality for characterizing soft tissue masses when radiographs are non-diagnostic or when clinical features are atypical. 1, 2, 4

Ultrasound indications:

• Atypical clinical presentation (fluctuant, warm, rapidly growing). 2
• Concern for ganglion cyst, tenosynovitis, or joint effusion. 1, 4
• Suspected abscess or soft tissue infection. 1, 4
• Ultrasound has 94.1% sensitivity and 99.7% specificity for superficial soft tissue masses. 2, 4

MRI with contrast is indicated if:

• Mass is >5 cm, deep-seated, or rapidly growing. 5, 2
• Ultrasound shows heterogeneous echotexture, increased vascularity, or irregular margins. 2
• There is concern for erosive OA, osteomyelitis, or malignancy. 1
• MRI provides superior soft tissue contrast and is the modality of choice for evaluating extent of disease and complications. 1

Step 4: Laboratory Testing (If Infection Suspected)

• Complete blood count, erythrocyte sedimentation rate, and C-reactive protein if infection is suspected. 1
• Joint aspiration under ultrasound or fluoroscopic guidance for culture and cell count if septic arthritis is a concern. 1

Management Approach

Conservative Management (First-Line for Heberden's Nodes)

The 2018 EULAR recommendations prioritize non-pharmacological and topical treatments for hand osteoarthritis. 1

• Patient education about the benign nature of Heberden's nodes and natural history of hand OA. 1
• Topical NSAIDs are first-line pharmacological treatment, preferred over systemic medications. 1
• Hand exercises and orthoses for symptomatic relief. 1
• Oral NSAIDs may be considered for symptom relief for limited duration if topical treatments are insufficient. 1
• Intra-articular glucocorticoids may be considered for painful DIP joints, though generally not recommended for hand OA. 1

Surgical Management

Arthrodesis (fusion) is the definitive surgical treatment for severe, symptomatic DIP joint osteoarthritis. 6, 7

Indications for surgery:

• Persistent pain despite conservative management. 6, 7
• Severe angular or rotational deformity. 6
• Functional impairment affecting quality of life. 6
• DIP fusions have high success rates, are well tolerated, and extremely durable. 6
• Mobility preservation is not a priority for DIP joints, unlike MCP or PIP joints. 7

When to Refer

• Refer to hand surgeon if conservative management fails after 3-6 months or if there is severe deformity. 1, 6
• Immediate referral to orthopedic oncology if mass is >5 cm, deep, rapidly growing, or has concerning imaging features. 5, 2
• Urgent referral if infection is suspected and patient has systemic symptoms or immunocompromise. 1

Critical Pitfalls to Avoid

• Do not assume all DIP swelling is benign Heberden's nodes without obtaining radiographs first. 1, 2
• Poor agreement exists between clinical Heberden's nodes and radiological DIP osteophytes (K statistic = 0.36), so radiographic confirmation is important. 3
• Do not perform biopsy before obtaining appropriate imaging (MRI) if there is any concern for malignancy, as this can compromise surgical margins. 5
• Ultrasound is operator-dependent and less accurate for deep masses; do not rely solely on ultrasound for definitive diagnosis. 2, 4
• Do not overlook signs of infection (warmth, erythema, systemic symptoms) that would require urgent evaluation and treatment. 1
• Radiographic severity does not always correlate with symptoms; base surgical decisions on clinical presentation and quality of life impact, not imaging alone. 7