Unilateral Arm or Leg Swelling: Causes, Evaluation, and Urgency

Sudden Unilateral Limb Swelling – Think Vascular/Lymphatic Emergency

Top Differential Diagnoses

Cause	Key Features	Urgency
Deep vein thrombosis (DVT)	Calf/thigh swelling, pain, warmth, erythema; Homan's sign unreliable. Risk: surgery, immobilization, cancer, OCPs, pregnancy, thrombophilia.	Urgent – US Doppler today
Cellulitis/lymphangitis	Spreading erythema, warmth, tenderness, fever; portal of entry (wound, tinea).	Urgent – antibiotics
Compartment syndrome	Pain out of proportion, paresthesia, pallor, pulselessness (late), tense swelling. Trauma, reperfusion, tight cast.	Emergent – fasciotomy
Lymphedema	Chronic, non-pitting, skin thickening; post-surgery/radiation (breast, pelvic), filariasis, congenital.	Subacute – referral
Ruptured Baker's cyst	Calf swelling, pain, crescent sign; mimics DVT. Knee OA/RA history.	Urgent – US to differentiate
Superficial thrombophlebitis	Tender, palpable cord along varicose vein; low embolism risk unless extends to deep system.	Semi-urgent
Venous insufficiency	Bilateral > unilateral; edema improves with elevation; varicosities, stasis dermatitis.	Chronic management
Heart/kidney/liver failure	Usually bilateral, dependent; orthopnea, JVD, ascites.	Treat underlying
Malignancy	Pelvic mass compressing iliac vein; axillary node dissection.	Urgent workup

Initial Evaluation

1. History: onset, trauma, surgery, cancer, meds, travel.
2. Exam: measure circumference (10 cm below tibial tuberosity / mid-thigh), compare sides; palpate popliteal/femoral nodes.
3. D-dimer if low/intermediate Wells score; if high → straight to US.
4. Duplex ultrasound = gold standard for DVT.

Red Flags – Go to ER

• Sudden severe pain, pallor, pulselessness, paralysis, paresthesia (compartment syndrome).
• Shortness of breath, chest pain, hemoptysis (PE).
• Rapidly spreading erythema, fever, sepsis signs.

Do not massage a swollen limb until DVT excluded. Elevate, immobilize, seek care.