Catastrophic antiphospholipid syndrome (CAPS): a rare, life-threatening clotting emergency

The NHS describes antiphospholipid syndrome (APS), sometimes called Hughes syndrome or sticky blood syndrome, as a rare autoimmune condition in which the immune system attacks proteins in the blood and makes the blood clot more easily. The main symptom of APS is a blood clot, which can happen anywhere in the body, and it is treated with medicines that help prevent blood clots.

CAPS is the most severe form. A published case report explains that APS can rarely progress to catastrophic APS, a life-threatening complication involving the development of multi-organ thromboses, and that unlike ordinary APS it is characterised by thrombosis in multiple organs within a short period of time. CAPS occurs in less than 1% of people with APS. The report notes that about 72% of patients in the cases it quoted were women with a mean age of 37, and that other autoimmune diseases such as lupus may be present.

The same report states that CAPS is usually due to an increase in the inflammatory response. The most common trigger is infection, followed by surgery, stopping anticoagulation, medication, obstetric complications and finally neoplasm (cancer). For people who already have APS, this is why the NHS advises speaking to your doctor before any medical procedure or starting new medicines, including contraception, because some medicines may not be safe and extra treatment or monitoring may be needed around procedures.

It is also why anticoagulant treatment is not stopped without medical advice. The NHS says most people with APS need to keep taking warfarin for the rest of their lives because of the high risk of another clot, and the report lists discontinuing anticoagulation among the recognised triggers of CAPS.

Because several organs can be affected at the same time, the picture can be dramatic and varied. In the case report, the patient was first admitted for pneumonia-related sepsis, kidney injury and encephalopathy before CAPS was recognised. The report lists common symptoms as fever, low platelets (thrombocytopenia), acute kidney failure, neurological deficits and disseminated intravascular coagulation, a widespread disturbance of clotting.

The NHS describes the symptoms of an ordinary clot that can be an early warning in anyone with APS: throbbing pain and swelling in one leg, pain and swelling in an arm or tummy, warm red or darkened skin over a painful area, and sudden breathing difficulty, chest pain and coughing up blood. It also lists a reddish-blue lace-like rash on the lower legs, easy bruising and joint pain among APS symptoms. In the single case reported, a woman who had never been diagnosed with APS presented with confusion, difficulty walking, hearing loss and skin changes.

The report notes that the most difficult thing about CAPS is that several patients present without any previous diagnosis of APS, which makes it challenging to diagnose on presentation and can delay treatment. Diagnosis is made in hospital from the clinical picture of multiple organs being affected over a short time, blood tests for antiphospholipid antibodies and clotting abnormalities, and imaging or tissue examination to show the small-vessel clots.

For ordinary APS, the NHS says that two blood tests three months apart are needed to confirm the diagnosis. In a CAPS emergency, doctors may need to act on the clinical picture while confirming tests are completed.

The case report states that treatment consists of triple therapy: anticoagulation to stop further clotting, glucocorticoids to damp inflammation, and therapeutic plasmapheresis (plasma exchange) or intravenous immunoglobulins. Because of the complexity and the life-threatening nature of the disease, a multidisciplinary team of various specialties is often necessary. Care is hospital-based and may involve support for failing organs.

The sources read for this page are one case report and the NHS APS page, so they do not describe second-line options in detail. People whose illness does not respond to first-line therapy may be offered other immune-modulating medicines under specialist guidance, which is a decision for the treating team.

The report states that mortality rates are as high as 50%, reflecting how serious the illness is, although outcomes depend on how quickly it is recognised and treated and on which organs are involved. People who survive an episode are managed as having APS with ongoing anticoagulant treatment and specialist follow-up.

The NHS recommends things that reduce the risk of blood clots in everyone with APS: regular exercise, a balanced diet, a healthy weight, drinking plenty of water, flight socks on long journeys, not smoking, limiting alcohol and not sitting for long periods without moving. It also advises speaking to your doctor before procedures or new medicines, and getting an urgent GP appointment or help from NHS 111 if you think you have a blood clot.