Difficult case: rituximab in anti-SRP antibody myositis in pregnancy.

A 30-year-old nulliparous woman presented at 15-week gestation with severe skeletal and respiratory muscle weakness, having been diagnosed with anti-signal recognition particle antibody myositis 3 years before. Remission had previously been induced with rituximab (after failure of standard therapies). She had continued oral prednisolone and rituximab every 6 months but had stopped this when planning pregnancy. At 16-weeks gestation, she restarted corticosteroids and rituximab, with clinical and biochemical recovery and no complications. Rituximab should ideally be given in the first trimester; treatment later in pregnancy increases the risk of neonatal B-cell depletion and cytopenias. The fetal risk from drug therapy must be weighed against the risk to mother and fetus from untreated disease. This report highlights the importance of preconception counselling for disease control and patient education regarding medication safety and early referral to obstetric medicine clinics, to facilitate complex clinical decision-making.