A 72-year-old man with hypertension and hyperlipidemia presents with sudden onset of severe pain in the left leg, pallor, pulselessness, and coldness. On examination, the left foot is mottled and cyanotic; femoral pulse is absent on the left. Right femoral pulse is palpable. He denies recent trauma. Doppler ultrasound shows no flow in the left superficial femoral artery. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis **Key Point:** The sudden onset of the **6 Ps** (Pain, Pallor, Pulselessness, Paresthesia, Paralysis, Perishing cold) in one leg with absent femoral pulse and no flow on Doppler indicates **acute arterial occlusion**. ## Differential Diagnosis of Acute Limb Ischemia | Feature | Acute Thrombosis | Acute Embolism | Dissection | AAA Rupture | |---------|------------------|----------------|-----------|-------------| | **Onset** | Sudden (hours) | Sudden (minutes) | Sudden | Sudden (catastrophic) | | **History** | Pre-existing PAD, claudication | AF, recent MI, cardiac source | Hypertension, Marfan syndrome | AAA, smoking, age >70 | | **Pulse** | Absent distally; proximal pulse may be present | Absent distally | Asymmetric pulses bilaterally | Absent bilaterally (shock) | | **Imaging** | Doppler: no flow in artery; CTA: thrombus in atherosclerotic vessel | Doppler: embolic occlusion | CTA: intimal flap, false lumen | CTA: rupture, hematoma | | **Systemic signs** | Localized to limb | Localized to limb | Chest/back pain, BP differential | Shock, hypotension, back pain | ## Why This Is Acute Thrombosis 1. **Unilateral presentation:** Absent left femoral pulse with patent right femoral pulse excludes aortic pathology (dissection, rupture). 2. **Localized ischemia:** Mottling and cyanosis confined to the left leg; no systemic shock or back pain. 3. **Doppler finding:** No flow in the superficial femoral artery indicates thrombosis, not embolism (which typically lodges at bifurcations). 4. **Risk factors:** Age, hypertension, hyperlipidemia—classic for atherosclerotic PAD with superimposed thrombosis. **High-Yield:** Acute thrombosis occurs when a **pre-existing atherosclerotic stenosis** (often asymptomatic or causing mild claudication) suddenly occludes due to: - Plaque rupture and thrombus formation - Reduced flow state (dehydration, heart failure, sepsis) - Hypercoagulability (malignancy, thrombophilia) ## Management of Acute Limb Ischemia ```mermaid flowchart TD A[Acute Limb Ischemia]:::outcome --> B{Viable limb?}:::decision B -->|Yes: No sensory loss, motor intact| C[Urgent revascularization]:::action C --> D[Angiography ± Thrombolysis/Thrombectomy]:::action B -->|Marginally viable: Sensory loss, weak motor| E[Revascularization + monitoring]:::action B -->|Non-viable: Sensory loss, paralysis, muscle rigidity| F[Amputation]:::urgent D --> G[Restore perfusion]:::outcome E --> H[Reassess at 6-12 hours]:::decision ``` **Clinical Pearl:** The **Rutherford Classification** stratifies acute limb ischemia: - **Stage I (Viable):** No sensory loss, no muscle weakness - **Stage II (Marginally viable):** Sensory loss in toes, weak plantarflexion - **Stage III (Irreversible):** Muscle rigidity, sensory loss, paralysis → amputation **Key Point:** Time is critical—revascularization must occur within **6–8 hours** to prevent irreversible tissue damage. This patient requires **urgent angiography with catheter-directed thrombolysis or mechanical thrombectomy**. [cite:Harrison 21e Ch 297; Norgren et al. TASC II]