Morales MH, Leigh CL, Simon EL. COVID-19 infection with extensive thrombosis: A case of phlegmasia cerulea dolens. Am J Emerg Med. 2020 May 15. Epub ahead of print.
“Cytokine storm has been implicated in COVID-19 and associated with severe infection , allowing for a focus on cytokine and other proinflammatory markers. It is suspected that the extensive release of cytokines causing a proinflammatory state may play a role in thrombus formation . Tanaka et al. reported that IL-6 could activate the coagulation cascade , increasing the risk of thrombosis and complication. Our patient did have an elevated level of IL-6, in addition to hypertension and elevated CRP, which are all independent risk factors for increased severity of COVID-19 infection .
Helms et al. found that 50 of 57 patients had positive lupus anticoagulant and antiphospholipid (aPL) antibodies , both of which have been associated with thrombotic complications.”
Shackford SR. (2018). Venous Disease. In: Abernathy’s Surgical Secrets, 7th ed.: p. 357.
What is the difference between phlegmasia alba dolens and phlegmasia cerulea dolens?
“These two entities occur following iliofemoral venous thrombosis, 75% of which occur on the left side presumably because of compression of the left common iliac vein by the overlying right common iliac artery (May-Thurner syndrome). Iliofemoral venous thrombosis is characterized by unilateral pain and edema of an entire lower extremity, discoloration, and groin tenderness. In phlegmasia alba dolens (literally, painful white swelling), the leg becomes pale. Arterial pulses remain normal. Progressive thrombosis may occur with propagation proximally or distally and into neighboring tributaries. The entire leg becomes both edematous and mottled or cyanotic. This stage is called phlegmasia cerulea dolens (literally, painful purple swelling). When venous outflow is seriously impeded, arterial inflow may be reduced secondarily by as much as 30%. Limb loss is a serious concern and aggressive management (i.e., venous thrombectomy, catheter-directed lytic therapy, or both) is necessary.”
Comerota AJ. Kasper GC. (2019). Compartment Syndrome and Venous Gangrene. In: Rutherford’s Vascular Surgery and Endovascular Therapy, 9th ed.: p. 2011.
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Figure 153.1 Clinical examples of phlegmasia alba dolens (A) and phlegmasia cerulea dolens (B and C).
“Most patients with iliofemoral DVT (IFDVT) present with swelling that involves the entire limb, causing varying degrees of discomfort. Phlegmasia alba dolens (see Fig. 153.1A) generally results from a more limited occlusion of the iliac veins, which causes leg discomfort and edema. However, the venous return is efficient enough to clear the dermal and subdermal venous blood before cyanosis occurs. The difference between phlegmasia alba dolens and PCD (see Fig. 153.1B and C) is the amount of deoxyhemoglobin in the venous plexus of the skin and subcutaneous tissue and the degree of discomfort produced by the associated venous hypertension and elevated compartment pressures. 
Cyanosis is caused by an increase in deoxyhemoglobin in the subdermal tissues at levels of 1.5 to 5 mg%.  With central deep venous occlusion leading to venous hypertension and sluggish venous return, there is stagnation of venous blood in the dermal and subdermal venous plexus, resulting in bluish discoloration of the leg.”
More PubMed results on PAD and PCD.