Systemic lupus erythematosus in a multiethnic US cohort (LUMINA):: XXIV.: Cytotoxic treatment is an additional risk factor for the development of symptomatic osteonecrosis in lupus patients:: results of a nested matched case-control study

Background: Osteonecrosis is common in systemic lupus erythematosus (SLE) and often disabling. The role of glucocorticoids in its development is well known. Objective: To explore other possible risk factors for osteonecrosis in SLE. Methods: A nested matched case-control study undertaken in the context of a large, longitudinal, multiethnic lupus cohort (LUMINA), currently formed of 571 SLE patients meeting American College of Rheumatology criteria. All those developing symptomatic osteonecrosis after the diagnosis of SLE were considered cases. Two controls matched for age, disease duration, ethnicity, and centre were selected for each case. Cases and controls were compared by univariable analyses using selected variables. Variables with p < 0.10 and those thought clinically relevant were entered into conditional logistic regression models including either the average dose or the highest dose of glucocorticoids, with osteonecrosis as the dependent variable. Results: 32 cases were identified and 59 matched controls selected (in five cases only one control could be found). By univariable analyses, both groups were largely comparable for socioeconomic-demographic, clinical, and laboratory variables. Cases were less exposed to hydroxychloroquine (as assessed by the percentage of exposure time) (p = 0.026), used higher doses of glucocorticoids (average and highest doses) (p = 0.011 and 0.001, respectively), and received cytotoxic drugs more often (p = 0.015). In the multivariable analyses only cytotoxic drug use (both models) and the highest dose of glucocorticoids remained associated with the occurrence of osteonecrosis. Conclusions: Cytotoxic drug use is a risk factor for the development of symptomatic osteonecrosis in SLE patients, along with glucocorticoids. No definite protective factors were identified.