What could be causing chronic pain and swelling on the thenar eminence of my left hand?

Chronic Thenar Eminence Pain with Recent Swelling: Diagnostic Approach

Start with plain radiographs (3 views) of the left hand immediately, followed by ultrasound if radiographs are normal or nonspecific, to evaluate for infection, compartment syndrome, retained foreign body, or soft tissue pathology. 1, 2

Initial Imaging Strategy

Begin with radiography as the first-line imaging study for chronic hand pain with swelling. 1 The standard radiographic examination includes posteroanterior, lateral, and oblique views to assess for:

• Fractures (acute or chronic/healed) 1
• Arthritis or joint space abnormalities 1
• Soft tissue swelling patterns 1
• Bone erosions or mineralization 1
• Retained foreign bodies (though ultrasound is more sensitive) 1

Critical Differential Diagnoses to Exclude Urgently

The 6-week progression from intermittent to daily pain with new swelling raises several time-sensitive concerns:

Compartment Syndrome of the Thenar Eminence

• This is a limb-threatening emergency that can occur spontaneously or from minor trauma. 3, 4
• Look for: firmness of the thenar eminence, pallor, coolness (poikilothermia), paresthesias of the thumb and index finger, and pain with passive thumb extension. 4
• Compartment syndrome occurs when tissue pressure exceeds perfusion pressure within the closed thenar compartment, leading to tissue necrosis if untreated. 3
• Even minor mechanisms can produce this syndrome—patients may initially dismiss symptoms as a "stinger." 3
• Requires emergent hand surgery consultation and fasciotomy if confirmed. 3, 4

Infection (Abscess or Cellulitis)

• Evaluate urgently for erythema, warmth, purulent drainage, or systemic signs (fever, elevated inflammatory markers). 5, 6
• Infections in edematous hands can progress rapidly and require immediate antibiotic therapy. 5
• Ultrasound can effectively identify abscesses and fluid collections. 2, 5

Retained Foreign Body

• Even after negative local exploration, foreign bodies can be missed on initial evaluation. 6
• Ultrasound is superior to radiography for detecting radiolucent foreign bodies (wood, plastic, organic material). 1, 2, 6

Next-Step Imaging: Ultrasound

If radiographs are normal or show only nonspecific findings, ultrasound of the hand is the next appropriate study. 1, 2

The American College of Rheumatology supports musculoskeletal ultrasound for patients without definitive diagnosis presenting with pain, swelling, or mechanical symptoms of the hand. 1, 2 Ultrasound advantages include:

• Identifies synovitis, joint effusion, tenosynovitis, tendinopathy, and tendon tears 1, 2
• Detects retained foreign bodies that cause infection 1, 2
• Allows dynamic assessment of tendons and soft tissues 2
• More readily available and less expensive than MRI 2
• Contributory to clinical assessment in 76% of patients with hand pain 1, 2

When to Consider MRI

MRI without IV contrast should be reserved for cases where ultrasound is inconclusive or deeper structures need evaluation. 2 However, MRI is of limited benefit in nonspecific hand pain. 1

MRI can demonstrate:

• Arthritis, tendinopathy, tenosynovitis 1
• Pulley injury, volar plate injury, chondral injury 1
• Ligament injuries 1

In one retrospective review, MRI changed clinical management in 69.5% of cases referred to hand surgeons, particularly by reassuring patients that no further follow-up was necessary in 70% of cases. 1

Specific Conditions to Consider

Chronic Exertional Compartment Syndrome

• Rare but documented in bilateral thenar compartments 7
• Characterized by activity-induced pain, swelling, and decreased muscle function 7
• Symptoms reproduced by repetitive gripping or manual activities 7
• Requires compartment pressure measurement for diagnosis 7

Tenosynovitis or Tendinopathy

• Ultrasound or MRI without IV contrast are equivalent first choices for evaluating tendon pathology. 1
• Both modalities can diagnose tendinopathy, tendon tears, stenosing tenosynovitis, and pulley injuries. 1

Clinical Pitfalls to Avoid

• Do not dismiss seemingly minor trauma mechanisms—internal muscle disruption can occur without obvious external injury. 3
• Do not rely solely on initial negative exploration—foreign bodies are frequently missed on first examination. 6
• Do not delay imaging if symptoms progress—compartment syndrome requires recognition within hours to prevent permanent impairment. 3, 4
• Assess for vascular compromise immediately: check digital pulses, capillary refill, skin temperature, and color. 5

Immediate Management Considerations

While pursuing diagnostic workup:

• Elevate and cool the extremity to limit swelling 3
• Remove any constrictive jewelry, watches, or wraps that could worsen compartment pressure 3
• Reassess within 48-72 hours to evaluate response and ensure no progression 5
• Refer urgently to hand surgery if compartment syndrome, deep infection, or vascular compromise is suspected 5, 3