What is the best course of action for a morbidly obese patient presenting with left foot pain and swelling for 2 days without injury, normal X-ray, and no skin changes?

Urgent Evaluation for Deep Vein Thrombosis

This morbidly obese patient with acute unilateral foot pain and swelling without trauma requires immediate compression ultrasonography to rule out deep vein thrombosis (DVT), as morbid obesity is a well-established high-risk factor for venous thromboembolism and this presentation is highly suspicious for DVT. 1

Immediate Diagnostic Workup

Calculate Clinical Probability

• Apply Wells score or DAYS score immediately to stratify DVT risk—morbid obesity, unilateral leg swelling, and absence of alternative diagnosis all increase probability 1
• Recent immobilization or limited mobility (common in morbidly obese patients) further elevates risk 2, 3

Obtain Compression Ultrasonography

• Order stat compression ultrasound of the entire left lower extremity—this is the diagnostic test of choice and should not be delayed in high-probability patients 1
• Morbid obesity increases technical difficulty but does not eliminate the need for this study 4

Laboratory Studies

• D-dimer if ultrasonography is delayed or clinical probability is low-to-moderate 2
• Complete blood count, basic metabolic panel
• Consider hemoglobin A1c given obesity and diabetes risk 5

Critical Differential Diagnoses to Exclude

Diabetic Foot Infection

• Examine for skin breaks, ulcers, or purulent drainage—infection requires ≥2 inflammatory signs (erythema, warmth, swelling, tenderness, purulent secretions) 5
• The absence of skin changes makes infection less likely, but carefully inspect between toes and plantar surfaces 6
• If diabetes is present or suspected, test protective sensation with monofilament 5

Charcot Neuro-osteoarthropathy

• CNO typically presents with minimal pain due to neuropathy—the presence of significant pain makes this less likely 1, 5
• If diabetic neuropathy is present, immediate immobilization is mandatory while awaiting imaging to prevent permanent deformity 5
• The normal X-ray argues against acute CNO, though early changes may be subtle 5

Cellulitis

• Requires presence of erythema, warmth, and tenderness—but the question states "no skin changes," making this diagnosis unlikely 5, 7
• If skin changes develop, blood cultures and inflammatory markers should be obtained 1

Vascular Assessment

• Palpate dorsalis pedis and posterior tibial pulses bilaterally—strong pulses exclude significant peripheral arterial disease 5
• Warm foot suggests adequate perfusion, further supporting DVT over arterial pathology 5

If DVT is Confirmed

Immediate Anticoagulation

• Initiate anticoagulation immediately with low-molecular-weight heparin (LMWH) or direct oral anticoagulant 1
• Standard fixed-dose LMWH regimens may be inadequate in morbidly obese patients—consider weight-adjusted dosing or anti-Xa monitoring 8
• Transition to oral anticoagulation for long-term secondary prophylaxis 1

Assess for Pulmonary Embolism

• Obtain CT pulmonary angiography if patient has chest pain, dyspnea, hemoptysis, or tachycardia 2, 3
• Morbidly obese patients with DVT have increased risk of concurrent pulmonary embolism 3

Hypercoagulable Workup

• Consider testing for factor V Leiden, prothrombin gene mutation, antiphospholipid antibodies, protein C/S deficiency if unprovoked DVT or recurrent events 2
• Multiple risk factors often coexist in morbidly obese patients 2

Disposition from Urgent Care

Transfer to Emergency Department if:

• DVT is confirmed on ultrasound—requires immediate anticoagulation and possible admission 1
• Signs of hemodynamic instability, severe symptoms, or suspected pulmonary embolism 1
• Critical limb ischemia (absent pulses, cold foot, pallor) 6

Outpatient Management if:

• Ultrasound is negative and alternative diagnosis is identified
• Patient is stable with low clinical probability and negative D-dimer

Common Pitfalls to Avoid

• Do not assume cellulitis without visible skin changes—unilateral leg swelling in morbid obesity is DVT until proven otherwise 1, 4
• Do not delay imaging for D-dimer results in high-probability patients—proceed directly to compression ultrasonography 1
• Do not use standard LMWH dosing without considering weight-based adjustments in patients with BMI >40 kg/m² 8
• Do not dismiss DVT because X-ray is normal—plain films do not visualize venous thrombosis 1
• Do not assume aspirin provides adequate anticoagulation if DVT is confirmed—full therapeutic anticoagulation is required 1