Autoimmune diseases magnify thromboembolism risk

All autoimmune diseases substantially increase the risk of pulmonary embolism and should be considered as hypercoagulable disorders that may benefit from preventive therapy, a new study has concluded.

Based on an analysis of the entire Swedish population, it identified more than 500,000 patients without a prior history of venous thromboembolism who were admitted to hospital because of an autoimmune disorder between 1964 and 2008. The researchers analysed 33 separate autoimmune conditions including rheumatoid arthritis, Crohn’s disease, type I diabetes, Addison’s disease and Graves’ disease.

In the year following the hospital admission, the overall risk of pulmonary embolism was six-fold higher in patients with autoimmune diseases compared to the general population.

The standardised incidence ratio (SIR) peaked at 16.4 in patients with polymyositis or dermatomyositis. It was also very high in those with immune thrombocytopenic purpura (10.8), polyarteritis nodosa (13.3) and SLE (10.2). The SIR was 6.0 in patients admitted because of rheumatoid arthritis, and 6.4 in those with type I diabetes.

Overall risk decreased with time, being 1.5 in years one to five after the hospital admission, and 1.15 at five to 10 years.

“The reduction in risk over time suggests that the thrombotic risk is linked to the inflammatory activity of the autoimmune disorders, which is likely to decrease because of treatment,” the researchers said.

“Efficient treatment of the inflammation… could therefore reduce the risk of pulmonary embolism and venous thromboembolism.”

Many previous studies had shown a link between autoimmune disorders and thromboembolism, but most had been relatively small and focused on a single disorder.

An editorial noted the very large scale of the study, and the fact that pulmonary embolism accounted for 5-10 per cent of all deaths in patients admitted to hospital for any reason.

“Anti-inflammatory drugs and thromboprophylaxis should be considered to treat inflammation associated with autoimmune disorders, particularly in people admitted to hospital,” it said. “However, prospective studies are needed to identify the predictive value of inflammatory markers for pulmonary embolism.”