Warfarin-Induced Skin Necrosis
A rare clotting reaction in the skin soon after starting warfarin
Quick Facts
- Type: Drug reaction / skin and clotting disorder
- Cause: Clotting in small skin blood vessels on starting warfarin
- Timing: Usually within the first days of treatment
- Seek urgent care: New painful, dark, or blistering skin patches
Overview
Warfarin-induced skin necrosis is a rare but serious complication that can occur soon after starting the blood thinner warfarin. Paradoxically, although warfarin is given to prevent clots, in this reaction tiny clots form in the small blood vessels of the skin and the fat just beneath it. This cuts off the blood supply to patches of skin, which become painful, discolored, and can break down.
The reaction usually appears within the first few days of treatment, often when warfarin is started at a high dose without an overlapping injectable blood thinner. It tends to affect areas with more fatty tissue, such as the breasts, thighs, buttocks, and abdomen. Because it can cause significant skin damage, prompt recognition and treatment are important.
Symptoms
Symptoms typically begin within the first three to ten days of starting warfarin and progress over hours to days.
- A painful, red or flushed patch of skin that appears suddenly
- Darkening of the area to a purple or black color as the skin loses its blood supply
- Blistering and, later, breakdown of the skin (necrosis)
- Common locations include the breasts, thighs, buttocks, and abdomen
The affected area can enlarge quickly, so any new painful, discolored skin patch after starting warfarin should be evaluated urgently.
Causes
The reaction is caused by a temporary imbalance in clotting factors when warfarin is first started.
- Early drop in natural anticlotting proteins: When warfarin begins, it lowers a natural anticlotting protein (protein C) faster than it lowers the clotting factors it is meant to reduce. This brief window favors clotting.
- Clots in small skin vessels: Tiny clots block the small blood vessels supplying the skin and underlying fat, leading to tissue damage.
- Underlying clotting tendencies: A pre-existing deficiency of protein C or protein S increases the risk.
Risk Factors
- Starting warfarin at a high loading dose without overlapping injectable anticoagulant
- An inherited deficiency of protein C or protein S
- Female sex and middle age (the reaction is reported more often in this group)
- Being treated for a clotting disorder
Diagnosis
Diagnosis is mainly clinical, based on the appearance and timing in relation to starting warfarin.
- Clinical assessment: The characteristic painful, discolored skin lesions appearing within days of starting warfarin strongly suggest the diagnosis.
- Skin biopsy: May be done to confirm clots in small skin vessels and rule out other causes of skin breakdown.
- Clotting studies: Tests for protein C and protein S levels and other clotting disorders, sometimes done after recovery.
Treatment
Treatment focuses on stopping the offending drug and managing both the clotting and the skin damage.
- Stop warfarin: Warfarin is discontinued immediately.
- Alternative anticoagulation: A different blood thinner, such as heparin, is used to maintain anticoagulation and reverse the temporary clotting imbalance.
- Vitamin K: May be given to counteract warfarin.
- Wound and skin care: Affected skin is cared for, and severe necrosis may need specialist wound care, surgical removal of dead tissue, or, rarely, reconstructive surgery.
People who have had this reaction usually need to avoid warfarin in the future and use alternative anticoagulants.
Prevention
- Starting warfarin gradually rather than with large loading doses
- Overlapping warfarin with an injectable anticoagulant such as heparin when first starting, which helps avoid the early clotting window
- Checking for known protein C or protein S deficiency in people at risk
- Recording any past reaction so warfarin is avoided in future care
When to See a Doctor
Seek urgent medical care if, within the first days to weeks of starting warfarin, you develop:
- A new, painful, red, purple, or darkening patch of skin
- Blistering or breakdown of an area of skin
- Rapidly enlarging skin discoloration, especially on the breasts, thighs, buttocks, or abdomen
Early treatment can limit the damage, so do not wait to have new skin changes evaluated. Tell the care team you have recently started warfarin.
Frequently Asked Questions
What is warfarin-induced skin necrosis?
It is a rare reaction in which small clots form in the blood vessels of the skin soon after starting warfarin, cutting off the blood supply so patches of skin become painful, discolored, and can break down. It usually appears in the first few days of treatment.
Why does a blood thinner cause clots in the skin?
When warfarin is first started, it lowers a natural anticlotting protein faster than the clotting factors it targets. This brief imbalance favors clotting, and tiny clots can block the small blood vessels supplying the skin, causing tissue damage.
Who is at risk of warfarin skin necrosis?
The risk is higher when warfarin is started at a high dose without an overlapping injectable blood thinner, and in people with an inherited deficiency of protein C or protein S. It is reported more often in middle-aged women, though it remains rare.
How is it treated?
Warfarin is stopped immediately, an alternative blood thinner such as heparin is used, and vitamin K may be given. The damaged skin is cared for, and severe cases may need specialist wound care or surgery. People usually avoid warfarin afterward.
Can warfarin skin necrosis be prevented?
Starting warfarin gradually rather than with large doses, overlapping it with an injectable blood thinner at the start, and identifying people with protein C or protein S deficiency all help reduce the risk. Past reactions should be clearly recorded.
References
- MedlinePlus, U.S. National Library of Medicine. Warfarin.
- American Society of Hematology. Anticoagulation therapy.
- Mayo Clinic. Warfarin side effects.