Low back pain as a presenting manifestation of antiphospholipid syndrome

Antiphospholipid syndrome (APS) is characterised by arterial, venous or microvascular thrombosis and/or pregnancy morbidity. Bone infarct, or avascular necrosis (AVN), is seen in up to 2.9% of patients with primary and secondary APS. Multiple bone infarcts, defined as involvement of three or more bony sites, are reported in 3%-10% of the patients with a history of corticosteroid use, systemic lupus erythematosus (SLE) and hypercoagulable states, including APS. The femoral head, knees, shoulders and ankles are commonly affected, while involvement of the ribs or vertebrae is rare. A young age of onset (≤30 years), an SLE damage index ≥1, a higher mean glucocorticoid dose, coexisting arthritis and a positive antiribonucleoprotein antibody are associated with a higher risk of AVN in a few SLE cohorts. In APS, thrombosis of the skeletal vessels is a possible mechanism for AVN in addition to trauma, dyslipidaemia, etc. Our patient, a young woman, presented with an acute onset of back pain, a new onset of accelerated hypertension and recurrent pregnancy loss. Over 1 month, she developed bone pain at multiple sites, including the distal radius, bilateral tibia and T11-L3 spine. A Tc 99 triple-phase bone scan revealed a bone infarct, and with further investigations, she was diagnosed with SLE with secondary APS. She was initiated on immunosuppression and anticoagulation.