Askling J et al. (2006) Risk for malignant lymphoma in ankylosing spondylitis: a nationwide Swedish case–control study. Ann Rheum Dis 65: 1184–1187

There is evidence that the risk of lymphoma is considerably elevated in patients with rheumatoid arthritis, but little is known about the risk of lymphoma in other inflammatory conditions. Askling et al. have conducted a population-based, case–control study in Sweden to examine the relationship between lymphoma and ankylosing spondylitis. They found, somewhat surprisingly, that there was no increased risk of lymphoma in patients with ankylosing spondylitis.

The researchers identified 50,615 patients from the Swedish Cancer Register who were diagnosed with Hodgkin's lymphoma, non-Hodgkin's lymphoma, or chronic lymphatic leukemia in 1964–2000. They also selected 92,928 controls from the Swedish census register, matched for age, sex, marital status, and county of residence. Overall, 23 patients and 41 controls had been diagnosed with lymphoma after having been hospitalized for ankylosing spondylitis. Analysis revealed no association between a history of ankylosing spondylitis and a diagnosis of lymphoma.

Despite the large study population, the number of patients included in the analysis was small, as only those hospitalized with ankylosing spondylitis were eligible; therefore, an increased risk of lymphoma cannot be ruled out in individuals with ankylosing spondylitis who have never been hospitalized. Moreover, despite the finding that average risk was not elevated, it is possible that lymphoma risk is increased in patients with severe ankylosing spondylitis.