A 52-year-old man with a 10-year history of essential hypertension presents with acute left leg swelling, pain, and cyanosis. On examination, the left leg is markedly edematous with a dusky, cyanotic appearance. Femoral venography shows extensive thrombosis of the iliac and femoral veins. Platelet count is 245,000/μL. Prothrombin time (PT) is 14 seconds (control 12 seconds), and activated partial thromboplastin time (aPTT) is 32 seconds (control 28 seconds). D-dimer is >10 μg/mL. Arterial blood gas shows pH 7.28, PaCO₂ 32 mmHg, HCO₃⁻ 14 mEq/L. What is the most likely diagnosis?

Explanation

## Clinical Presentation & Pathophysiology This patient presents with the classic triad of **phlegmasia cerulea dolens (PCD)**: 1. **Acute, massive leg swelling** — left leg markedly edematous 2. **Cyanosis and dusky discoloration** — due to venous congestion and tissue hypoxia 3. **Severe pain** — from ischemia and tissue hypoxia **Key Point:** Phlegmasia cerulea dolens is a medical emergency representing the most severe form of acute deep vein thrombosis (DVT), characterized by extensive venous thrombosis that compromises both venous return AND arterial perfusion. ## Pathophysiology of PCD ```mermaid flowchart TD A[Extensive iliofemoral DVT]:::outcome --> B[Massive venous obstruction] B --> C[Venous pressure rises acutely] C --> D[Venous return severely impaired] D --> E[Tissue edema and congestion] E --> F[Cyanosis and dusky discoloration]:::outcome C --> G[Venous pressure exceeds arterial pressure] G --> H[Arterial perfusion compromised]:::urgent H --> I[Tissue ischemia and necrosis] I --> J[Limb-threatening emergency]:::urgent J --> K[Risk of gangrene without urgent intervention] ``` **High-Yield:** The pathophysiology is **venous hypertension leading to arterial insufficiency**, not primary arterial occlusion. The massive venous thrombosis raises venous pressure so high that it exceeds capillary and arteriolar pressure, causing arterial inflow to cease despite patent arteries. ## Clinical Features of PCD vs. Other Differentials | Feature | Phlegmasia Cerulea Dolens | Arterial Occlusion | Compartment Syndrome | HIT | |---------|---------------------------|-------------------|----------------------|-----| | **Onset** | Hours (acute DVT) | Sudden | Hours (post-trauma/surgery) | Days (HIT-II) | | **Edema** | Massive, pitting | Minimal | Tense, firm | Variable | | **Color** | Dusky cyanosis | Pale, mottled | Normal/pale | Normal | | **Pulses** | Present initially | Absent | Present | Present | | **Venography** | Extensive DVT | Arterial cut-off | Normal vessels | May show DVT/PE | | **Platelet count** | Normal/high | Normal | Normal | **↓ (HIT hallmark)** | | **PT/aPTT** | Prolonged (DIC) | Normal | Normal | Prolonged (HIT) | | **D-dimer** | Markedly elevated | Elevated | Normal/mild ↑ | Markedly elevated | **Clinical Pearl:** In this patient, the **normal platelet count (245,000/μL) excludes HIT**, which typically presents with thrombocytopenia (often <50,000/μL in HIT-II). The **prolonged PT and aPTT with markedly elevated D-dimer suggest DIC secondary to massive thrombosis**, not primary coagulopathy. ## Why This Is PCD, Not Arterial Occlusion **Key Point:** The presence of **palpable pulses** (implied by the clinical description and the absence of the classic "5 Ps" of acute arterial occlusion) and **extensive venous thrombosis on venography** confirm venous, not arterial, pathology. Arterial occlusion would show: - Absent pulses - Pale, not cyanotic, limb - Normal venography - Acute arterial cut-off on angiography ## Metabolic Derangement The arterial blood gas shows: - **pH 7.28** — metabolic acidosis - **HCO₃⁻ 14 mEq/L** — low bicarbonate - **PaCO₂ 32 mmHg** — respiratory compensation (hyperventilation) **Clinical Pearl:** This metabolic acidosis reflects **tissue ischemia and anaerobic metabolism** from the compromised microcirculation, consistent with PCD. The body is attempting respiratory compensation by hyperventilating to blow off CO₂. ## Immediate Management **High-Yield:** PCD is a **limb-threatening emergency** requiring: 1. **Immediate anticoagulation** — IV unfractionated heparin (bolus 80 units/kg, then infusion) 2. **Leg elevation and analgesia** 3. **Urgent vascular surgery consultation** — for consideration of: - **Catheter-directed thrombolysis (CDT)** — preferred if no contraindications - **Mechanical thrombectomy** — if thrombus burden is massive - **IVC filter** — if PE risk is high and thrombolysis contraindicated 4. **Correction of metabolic acidosis** — IV fluids, treatment of underlying cause 5. **Monitoring for compartment syndrome** — may develop as edema worsens **Warning:** Delay in treatment can result in limb gangrene and amputation. Mortality is 5–10% even with treatment; amputation rate is 10–40%. ## Distinction from Phlegmasia Alba Dolens **Mnemonic:** **PAD = Pale And Dolens** (white leg); **PCD = Cyanotic and Dolens** (blue leg) - **Phlegmasia alba dolens** — white, painful leg from massive DVT with preserved arterial flow (less severe) - **Phlegmasia cerulea dolens** — blue, painful leg from massive DVT with compromised arterial flow (more severe, limb-threatening) This patient has the **blue (cyanotic) variant**, confirming PCD. [cite:Harrison 21e Ch 111; Robbins & Kumar 10e Ch 4]