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What is Phlegmasia cerulea dolens and explain in detail?
Phlegmasia cerulea dolens (PCD) (literally: painful blue inflammation), not to be confused with preceding phlegmasia alba dolens, is an uncommon severe form of lower extremity deep venous thrombosis (DVT) that obstructs blood outflow from a vein. Upper extremity PCD is less common, occurring in under 10% of all cases. PCD results from extensive thrombotic occlusion (blockage by a thrombus) of extremity veins, most commonly an "iliofemoral" DVT of the iliac vein and/or common femoral vein. It is a medical emergency requiring immediate evaluation and treatment.

Symptoms and signs
Primary symptoms
It is characterized by progressive lower extremity edema distal to the thigh, tight shiny skin, cyanosis (inadequate blood oxygenation), petechiae or purpura, and sudden severe pain of the affected limb in proportion to the level of venous blockage.  Patients often have difficulty walking. Blisters, bullae, paresthesias, and motor weakness may develop in severe cases, along with gangrene in ~50% of cases. Distal pulses are palpable early on but may diminish over time, and doppler signal can be usually heard throughout disease progression