Background/Purpose:

The trigger for a thrombotic in patients with antiphospholipid antibodies is unknown. Thrombocytopenia is among the most common clinical manifestations of the Antiphospholipid antibody syndrome (APS). The purpose of this study was to investigate whether patients with lupus and positive antiphospholipid profile with thrombocytopenia are at more risk to have obstetric or thrombotic events than patients with antiphospholipid but without thrombocytopenia.

Methods:

Patients with SLE and positive antiphospholipid (aPL) profile (Lupus anticoagulant (LA), anticardiolipin (aCL) antibody of IgG and/or IgM isotype or anti-β₂ glycoprotein-I antibody of IgG and/or IgM isotype) and chronic thrombocytopenia (Platelet count<100,000) confirmed for 2 consecutive clinic visits followed at the prospective longitudinal lupus cohort since 1996 were recruited (study group). As controls a group of patients with SLE with positive aPL without thrombocytopenia were selected and matched by sex, age of SLE diagnosis, age at study start, disease duration and length of follow up period. Patients in the lupus cohort are followed at 2-6 month intervals according to a standard protocol which documented the presence of thrombotic events and obstetric morbidity as defined by the revised Sapporo criteria of APS. Descriptive analysis was used to describe the patients. Kaplan-Meier (KM) curves was used to compare time to 1st event between study groups.

Results:

The study group included 21 patients and 63 controls, 81% were females with a mean age of 39.8 ± 13.0 years and age of SLE diagnosis at 31.7 ± 14.7 years. The mean disease duration was 8.1 ± 7.8 years and they were followed for an average of 12.1 ± 9.3 years.

During the study period, the medication used by cases and controls respectively  were: on steroids 86% vs  79% (p=.075); on antimalarials 43% vs 68% (p=0.07); on immunosuppressants 52% vs 43% (p=0.46); on ASA 20% vs 22% (p=1.00); and on anticoagulants 5% vs 10% (p=0.67).

16 events occurred in the study group compared to 43 events in the controls and included 6 Obstetrical morbidities in 2 patients in the study groups compared to 4 events in 2 patients in the controls (KM  p=0.17), 9 arterial thrombosis in 4 patients in the study group compared to 24 events in 17 patients  in the controls (KM p=0.19) and 1 event of venous thrombosis in 1 patient in the study group compared to 15 events in 10 patients  in the controls (KM p=0.19).

Figure 1- The Kaplan-Meier curve for time to 1^st event after Study Start.

Conclusion:

Thrombocytopenia in patients with antiphospholipid antibodies in SLE is not associated with increased thrombotic events.