What is the differential diagnosis for a healthy 36-year-old female with swelling and pain on the top of her left foot in the distal metatarsal area, without any history of injury?

Differential Diagnosis: Dorsal Foot Pain and Swelling in Healthy 36-Year-Old Female

In a healthy 36-year-old woman with atraumatic dorsal metatarsal pain and swelling, stress fracture is the most likely diagnosis and must be ruled out first, followed by inflammatory conditions including extensor tendinitis, metatarsophalangeal joint synovitis, and ganglion cyst.

Primary Differential Diagnoses

Most Likely: Stress Fracture

• Stress fractures are the leading cause of severe metatarsal pain in active adults, even without recalled trauma 1
• Initial radiographs miss 44-88% of stress fractures early in their course, with sensitivity ranging only 12-56% 2, 1
• The second and third metatarsals are most commonly affected due to repetitive loading during gait 3
• Clinical features include point tenderness over the metatarsal shaft, pain with weight-bearing, and localized swelling 1

Extensor Tendinitis

• Inflammation of the extensor digitorum longus or extensor hallucis longus tendons causes dorsal foot pain and swelling 3
• Often related to overuse, tight footwear, or changes in activity level
• Pain worsens with toe extension against resistance
• Ultrasound can demonstrate tendon thickening and peritendinous fluid 3

Metatarsophalangeal (MTP) Joint Synovitis

• Inflammatory synovitis of the MTP joints presents with dorsal swelling and pain 4, 5
• May progress to plantar plate insufficiency if untreated
• Second MTP joint is most commonly affected 3
• Pain typically worsens with weight-bearing and toe dorsiflexion 4

Ganglion Cyst

• Dorsal foot ganglion cysts arise from joint capsules or tendon sheaths 3
• Present as visible or palpable swelling with variable pain
• MRI or ultrasound confirms the diagnosis and shows fluid-filled cystic structure 3

Less Common but Important Considerations

Freiberg's Infraction (osteochondrosis of metatarsal head):

• Typically affects the second metatarsal head in young adults 1
• Presents with dorsal swelling and pain over the affected metatarsal head
• Radiographs may show flattening or sclerosis of the metatarsal head 2

Intermetatarsal Bursitis:

• Can cause dorsal swelling that extends from the plantar intermetatarsal space 1
• Often mimics Morton's neuroma but with more prominent swelling 2

Early Inflammatory Arthropathy:

• Rheumatoid arthritis or seronegative spondyloarthropathy can present with isolated MTP joint involvement 4
• Consider if there are systemic symptoms or morning stiffness

Algorithmic Diagnostic Approach

Step 1: Obtain Weight-Bearing Plain Radiographs Immediately

• Order three-view weight-bearing radiographs of the foot (AP, oblique, lateral) as the first-line imaging study 2, 1, 6
• Weight-bearing views are essential for proper evaluation of foot structures and pressure distribution 1
• Radiographs can identify fractures, dislocations, osteoarthritis, and bony deformities with specificity of 88-96% 2
• Look specifically for: cortical breaks, periosteal reaction, sclerosis, joint space narrowing, and soft tissue swelling 1

Step 2: If Radiographs Are Negative but Clinical Suspicion Remains High

• Proceed directly to MRI of the foot without contrast 1
• MRI is the gold standard for detecting occult stress fractures, soft tissue pathology, and bone marrow edema 1, 3
• MRI has superior soft tissue contrast and can identify tendinitis, synovitis, ganglion cysts, and early osteochondral lesions 3
• Do not wait weeks for repeat radiographs if clinical suspicion is high—early MRI changes treatment and prevents complications 1

Step 3: Consider Ultrasound as Alternative for Soft Tissue Evaluation

• Ultrasound is operator-dependent but useful for evaluating extensor tendons, bursitis, and ganglion cysts 2, 3
• Provides dynamic assessment and excellent clinical correlation 3
• Less expensive and more readily available than MRI 2

Critical Clinical Features to Elicit

Activity and Footwear History

• Recent increase in physical activity, running, or walking distance suggests stress fracture 1
• New or tight footwear can cause extensor tendinitis or pressure-related inflammation 1
• Occupational factors: prolonged standing or repetitive foot movements 4

Physical Examination Findings

• Point tenderness over metatarsal shaft strongly suggests stress fracture 1
• Pain with passive toe extension indicates extensor tendinitis
• Palpable mass suggests ganglion cyst 3
• Warmth and diffuse swelling over MTP joint suggests synovitis 4
• Pain with MTP joint compression (squeeze test) indicates joint pathology 3

Weight-Bearing Ability

• Complete inability to bear weight raises concern for complete fracture 2
• Pain only with prolonged weight-bearing is more consistent with stress reaction or tendinitis 1

Critical Pitfalls to Avoid

Do Not Rely on Initial Radiographs Alone

• Normal radiographs do not exclude stress fracture—they miss 44-88% of cases early in the course 2, 1
• If clinical suspicion is high based on point tenderness and activity history, proceed to MRI even with normal x-rays 1

Do Not Order Ankle Radiographs for Metatarsal Pain

• Ankle films will not properly visualize the metatarsals or MTP joints 1
• Specifically request foot radiographs with weight-bearing views 2, 1

Do Not Dismiss Atraumatic Presentation

• Stress fractures occur from repetitive microtrauma without a single recalled injury 1
• Many patients do not recognize gradual activity increases as causative 2

Do Not Delay Advanced Imaging in Active Patients

• Early diagnosis of stress fracture prevents progression to complete fracture 1
• Delayed diagnosis increases healing time and risk of complications 2

When to Consider Alternative Diagnoses

If Systemic Symptoms Present

• Morning stiffness >30 minutes, involvement of other joints, or constitutional symptoms warrant rheumatologic workup 4
• Inflammatory markers (ESR, CRP) and rheumatoid factor may be indicated

If Visible Mass Present

• Palpable or visible swelling that is distinct from diffuse edema suggests ganglion cyst or soft tissue tumor 3
• Ultrasound or MRI can characterize the lesion 3

If Pain Pattern Atypical

• Burning or electric shock-like pain radiating to toes suggests nerve pathology (though typically plantar, not dorsal) 2
• Night pain or pain at rest raises concern for infection or tumor (rare in healthy young adults)