The two most common skin conditions associated with APS are:
About a fifth of APS patients have a skin condition called livedo reticularis, that seems to affect women more than men.
Livedo reticularis is caused by tiny clots that develop inside the blood vessels of the skin that reduce the blood flow. It creates a red or blue blotchy, lacy pattern usually on the knees, thighs and upper arms, but can also appear on the body. In some patients it can be quite widespread. The condition is often more severe in cold weather.
Poor circulation, especially in the lower part of the legs, can sometimes cause skin ulcers.
Skin ulcers usually occur over the ankles and feet, and it is estimated that they will develop in up to a third of APS patients. In the past, it was believed that these leg ulcers resulted from DVTs, but it is now known that they sometimes occur even if the person has not had a DVT. The ulcers usually appear as small, painful wounds that often heal quickly when anticoagulation treatment is started. However, in some cases, they do not respond well to treatment and can grow quite large in size.
In addition to these two well-recognised symptoms, in a very small minority of patients, skin necrosis can occur.
Skin necrosis means the skin tissue in a very small area of the body, usually on the face, arms, legs or buttocks dies due to a lack of blood and oxygen supplied to the affected area. The symptoms begin with a skin eruption which then becomes black. In very rare cases, gangrene can develop in the fingers or toes as the tissue loses all the blood supply and begins to decay. Patients who do develop skin necrosis tend to also have other autoimmune conditions such as Raynauds while gangrene is often associated with catastrophic APS.
The nails can also be affected in a small number of patients with APS. Small lines of blood, known medically as splinter haemorrhages, appear as little red or brown streaks underneath the nail. They result from clots that damage the tiny blood vessels and tend to appear in several nails.