What causes single finger swelling?

Single Finger Swelling: Differential Diagnosis and Evaluation

Single finger swelling requires immediate assessment for pyogenic flexor tenosynovitis (PFT), which is a surgical emergency that can lead to finger amputation or death if not recognized and treated urgently. 1

Immediate Life- and Limb-Threatening Causes

Pyogenic Flexor Tenosynovitis

• PFT presents with the four Kanavel signs: symmetrical swelling of the affected finger, finger held in flexed position, pain with passive extension, and tenderness along the flexor tendon sheath. 1
• Radiographic measurement showing volar soft tissue thickness minus dorsal soft tissue thickness ≥7 mm at the proximal phalanx level has 82% positive predictive value for PFT (sensitivity 84%, specificity 74%). 2
• A difference of ≥10 mm predicts PFT with 76% probability. 2
• This is a surgical emergency requiring immediate intravenous antibiotics and emergent hand surgery consultation. 1
• Typically occurs after penetrating trauma to the volar aspect of the digit and rapidly propagates through the flexor tendon sheath. 1

Septic Arthritis

• Initial radiographs may show soft tissue swelling, joint effusion, or be normal in early infection (<14 days). 3
• Image-guided aspiration with culture is essential for definitive diagnosis when imaging cannot distinguish infected from noninfected joints. 3
• CT with IV contrast can assess soft tissue extent and guide aspiration or surgical debridement. 3

Inflammatory and Rheumatologic Causes

Dactylitis ("Sausage Digit")

• Psoriatic arthritis causes painful, swollen joints with characteristic dactylitis affecting individual fingers, which may involve just one ray. 3, 4
• Recent ultrasound and MRI studies demonstrate that dactylitis results from flexor tenosynovitis, not necessarily joint capsule enlargement. 5
• The diffuse painful swelling creates the characteristic "sausage-like" appearance. 5

Erosive Hand Osteoarthritis

• Targets interphalangeal joints with inflammatory symptoms including soft tissue swelling, erythema, paresthesias, and mildly elevated CRP levels. 3, 4
• Typically has abrupt onset with marked pain and functional impairment. 3
• Distinguished by radiographic subchondral erosion on plain films. 3

Juvenile Rheumatoid Arthritis

• Isolated finger swelling as initial presentation of JRA leads to significant diagnostic delay (mean 8 months vs 3.4 months for typical onset). 6
• 57% of patients with isolated digital swelling progress to polyarticular disease, compared to only 15% with typical large-joint onset. 6
• Consider in children under 16 years with persistent single finger swelling. 6

Gout

• Gouty tenosynovitis may present with symptoms resembling infection and can coexist with actual infection, creating a diagnostic and therapeutic challenge. 7
• Normal or relatively low serum uric acid levels do not exclude gout—synovial fluid crystal analysis is pivotal. 7
• May superimpose on pre-existing hand osteoarthritis. 3
• When complicated by infection (particularly MRSA), standard therapies may fail due to ongoing crystal-induced inflammation, potentially requiring amputation. 7

Infectious Causes Beyond PFT

Soft Tissue Abscess

• Radiographs may show soft tissue swelling, effacement of fat planes, gas, or foreign bodies. 3
• CT with IV contrast can differentiate cellulitis, myositis, tenosynovitis, and abscess. 3
• Image-guided aspiration allows for safe drainage and culture while reducing risk of contaminating adjacent normal tissues. 3

Retained Foreign Body with Secondary Infection

• Obtain radiographs first, especially if foreign body composition is unknown—metal, graphite, and stone are radiodense. 3
• Ultrasound is optimal for radiolucent material (plastic, wood) and allows precise localization. 3
• Glass is inconsistently visible radiographically, particularly small fragments. 3
• Retained material triggers granulomatous reaction with subsequent soft tissue infection. 3

Osteomyelitis

• MRI is the preferred imaging modality with high sensitivity and specificity; importantly, a negative MRI excludes osteomyelitis. 3
• Early acute osteomyelitis (<14 days) may show only mild soft tissue swelling on radiographs. 3
• Chronic osteomyelitis shows bone sclerosis on radiographs. 3

Vascular Causes

Upper Extremity Deep Vein Thrombosis (UEDVT)

• Unilateral swelling indicates obstruction at the level of brachiocephalic, subclavian, or axillary veins requiring urgent evaluation. 4
• Presents with ipsilateral upper-extremity edema, pain, and paresthesia. 4
• Duplex ultrasound is the initial imaging modality with sensitivity and specificity above 80%. 4
• Highest risk with indwelling venous devices (catheters, pacemakers, defibrillators). 4

Diagnostic Algorithm

Step 1: Assess for Surgical Emergency

• Examine for Kanavel signs—if present, initiate IV antibiotics and obtain emergent hand surgery consultation immediately. 1
• Obtain plain radiographs to measure volar-dorsal soft tissue thickness difference at proximal phalanx level. 2
• Systemic symptoms (fever, chills) may be present but are not required for diagnosis. 1

Step 2: Determine Unilateral vs Bilateral Distribution

• Unilateral single finger swelling suggests local obstruction, trauma, infection, or monoarticular inflammatory process. 4
• Bilateral hand involvement suggests systemic causes (see separate evaluation pathway). 8

Step 3: Obtain Targeted History

• Recent trauma, puncture wound, or penetrating injury to volar finger surface. 3, 1
• Indwelling venous devices or recent upper extremity procedures. 4
• Aquatic exposure or occupational water immersion (chronic paronychia). 4
• Known inflammatory arthritis, psoriasis, or gout. 3, 4
• Age under 16 years (consider JRA). 6

Step 4: Initial Imaging

• Plain radiographs in two planes are mandatory for any musculoskeletal pathology with swelling. 3
• Radiographs exclude fractures, tumors, detect foreign bodies, and provide baseline for future imaging interpretation. 3
• Measure soft tissue thickness if PFT suspected. 2

Step 5: Advanced Imaging When Indicated

• MRI if osteomyelitis suspected after radiographs—negative MRI excludes osteomyelitis. 3
• Ultrasound for suspected radiolucent foreign body or to guide aspiration. 3
• CT with IV contrast to assess soft tissue extent and differentiate cellulitis from abscess. 3
• Duplex ultrasound if UEDVT suspected based on risk factors. 4

Step 6: Aspiration and Culture

• Image-guided aspiration is essential when imaging cannot distinguish infected from noninfected joints or fluid collections. 3
• Culture allows identification of organism and directly affects treatment. 3
• Synovial fluid crystal analysis is pivotal if gout suspected, especially with normal serum uric acid. 7

Common Pitfalls to Avoid

• Do not dismiss uniform finger swelling as excluding PFT—all finger infections cause diffuse swelling; PFT is distinguished by differential volar vs dorsal thickness. 2
• The term "fusiform swelling" is a misnomer for acute PFT because the finger is not spindle-shaped. 2
• Do not rely on serum uric acid to exclude gout—normal levels do not exclude the diagnosis. 7
• Do not delay diagnosis in children with isolated finger swelling—JRA presenting this way has worse prognosis with 57% progressing to polyarticular disease. 6
• Do not assume single pathology—gout and infection can coexist, requiring simultaneous treatment of both conditions. 7
• Do not obtain MRI in suspected PFT—this is a clinical diagnosis requiring immediate surgical consultation, not advanced imaging. 1

Follow-Up Protocol

• Reassess within 48-72 hours to evaluate response to initial management and ensure no progression. 4
• Schedule formal evaluation at 6 weeks if swelling persists to detect delayed complications or underlying pathology. 4
• If UEDVT confirmed, initiate therapeutic anticoagulation immediately following standard DVT treatment protocols. 4
• For inflammatory arthritis, refer to rheumatology for disease-modifying therapy. 8