Pathophysiology of neonatal lupus
NL is associated with the transplacental passage of maternal anti-Ro/SS-A and anti-La/SS-B IgG antibodies. One or more clinical manifestations of NL occurs in 25% to 30% of infants whose mothers have one or both of these antibodies regardless of their underlying disease. The most frequent abnormalities are photosensitive rash (lesions of discoid lupus or subacute cutaneous lupus), hepatic dysfunction, neutropenia, and thrombocytopenia. Congenital heart block (CHB) is of most concern, is identified most often between 18 and 28 weeks of gestation, and is associated with anti-Ro/SS-A antibodies (especially anti-Ro52). The cutaneous, hepatic, and hematologic manifestations are transient, generally resolving within 2 to 6 months after delivery, whereas heart block (typically third degree) is frequently permanent and may require a pacemaker. The overall risk of CHB is 2% but is increased to 18% in an anti-Ro/SS-A-positive mother who has had a previous child with CHB. Mothers with these antibodies are screened with serial weekly pulsed-Doppler echocardiograms/obstetric ultrasounds starting at 16 weeks through 28 weeks of gestation. Development of first-degree heart block (controversial), second-degree heart block, or a pericardial effusion in the fetus is treated with fluorinated steroids that cross the placenta (dexamethasone, betamethasone). Once third-degree heart block has developed, it cannot be reversed with medications and the infant will require a pacemaker. Fetal mortality is 20% in those who develop CHB and a cardiomyopathy (fetal hydrops) in utero. Hydroxychloroquine may reduce the risk of NL and is prescribed during pregnancy starting at 6 weeks of gestation for all SLE patients who have had a previous child with CHB due to NL. Some clinicians recommend treating all anti-Ro/SS-A-positive SLE patients with hydroxycloroquine during any (including first) pregnancy in an attempt to prevent NL and CHB in the fetus (controversial).