What is the appropriate evaluation and management for a patient presenting with unilateral foot swelling?

Unilateral Foot Swelling: Evaluation and Management

Immediate Priority: Exclude Life-Threatening Diagnoses

Deep vein thrombosis (DVT) is the most critical diagnosis to exclude first in any patient presenting with unilateral foot swelling, as it carries significant morbidity and mortality risk if untreated. 1, 2

Clinical Assessment for DVT

• Classic DVT presentation includes ipsilateral extremity edema, pain, heaviness distal to thrombosis, and unexplained persistent calf cramping 2
• Risk factors include indwelling venous devices, cancer, postoperative state, hypercoagulability, heart failure, advanced age, and trauma 2
• Critical pitfall: Do not rely on absence of warmth or redness to exclude DVT—these signs may be absent 2

Diagnostic Algorithm Based on Clinical Probability

For high pretest probability patients (recent surgery, immobilization, cancer, or multiple risk factors):

• Proceed directly to ultrasound duplex Doppler without D-dimer testing 1, 2
• The American College of Radiology recommends ultrasound duplex Doppler as initial imaging with diagnostic sensitivities and specificities above 80% 1
• If ultrasound is positive, initiate anticoagulation immediately without confirmatory venography 2

For low-to-moderate pretest probability patients:

• Begin with highly sensitive D-dimer testing 2
• If D-dimer is negative, no further testing needed 2
• If D-dimer is positive, proceed to proximal compression ultrasound or whole-leg ultrasound 2

Exclude Infection as Second Priority

Infection requires at least two of the following clinical signs: local swelling/induration, erythema, local tenderness/pain, local warmth, or purulent discharge. 3, 1

Key Assessment Points for Infection

• Critical pitfall: Fever, elevated white blood cell count, or elevated C-reactive protein may be absent in up to half of patients with significant infections 1
• In diabetic patients, examine carefully between toes and plantar surfaces, as infection may be subtle 3
• Purulent secretions or nonpurulent discharge with friable/discolored granulation tissue suggest infection 3

Obtain Plain Radiographs in All Cases

• The American College of Radiology recommends three-view radiographs (AP, oblique, lateral) of the foot to evaluate for fractures, dislocations, bone destruction, or foreign bodies 1
• This is essential baseline imaging regardless of suspected etiology 1

Special Consideration: Diabetic Patients

In diabetic patients with neuropathy presenting with unilateral red, warm, swollen foot with intact skin, always suspect active Charcot neuro-osteoarthropathy after excluding infection, gout, and DVT. 2

Charcot Foot Assessment

• Critical pitfall: Never assume absence of pain rules out serious pathology in diabetic patients with neuropathy—pain may be minimal or absent due to sensory neuropathy 1
• Temperature asymmetry >2°C between limbs suggests active inflammatory process 2
• Immediate subspecialist referral required for suspected active Charcot neuro-osteoarthropathy to prevent progression to deformity and ulceration 1
• If X-rays are negative but clinical suspicion remains, MRI is the preferred modality 1

Evaluate for Vascular Insufficiency

• Assess for arterial ischemia by checking pedal pulses bilaterally 3
• If one or more pedal pulses are absent, measure ankle-brachial pressure index 3
• Ankle-brachial pressure index <0.9 indicates peripheral arterial disease 3
• Important caveat: Ankle pressure might be falsely elevated due to arterial calcification in diabetic patients; toe pressure or transcutaneous oxygen pressure (TcPo2) measurements are more reliable 3

Assess for Venous Insufficiency

• Evaluate for chronic venous disease with duplex ultrasound assessing direction of blood flow, venous reflux, and deep venous system 2
• Look for skin changes suggesting chronic venous stasis 2

Examine Footwear and Biomechanics

• Meticulously examine shoes in all patients, as ill-fitting shoes are the most frequent cause of foot pathology even in patients with vascular disease 3
• Assess for foot deformities, calluses, or areas of abnormal loading 3
• In high-risk patients (neuropathy, ischemia, deformities), refer for specialized footwear evaluation 3

When to Refer Urgently

• Suspected DVT with positive ultrasound: immediate anticoagulation and possible hospital admission if hemodynamically unstable 4
• Suspected active Charcot neuro-osteoarthropathy: immediate subspecialist referral 1
• Suspected osteomyelitis (bone visible or palpable with sterile probe, chronic ulcer >6 weeks): refer for possible bone biopsy 1
• Evidence of deep-space infection, abscess, or limb-threatening infection: urgent surgical consultation 1
• Critical limb ischemia (absent pulses, cold foot, pallor): immediate emergency department transfer 4

Alternative Diagnoses to Consider

If DVT and infection are excluded:

• Lymphedema (may be secondary to tumor compression, radiation, or surgery) 2
• Heart failure causing increased capillary hydrostatic pressure 2
• Hypoproteinemia from liver or renal disease 2
• Lipedema (bilateral subcutaneous adipose tissue deposition, though can appear asymmetric) 5
• May-Thurner syndrome (compression of left iliac vein, typically presents with left lower limb swelling) 6