Two infants born to mothers with pregnancy-related polymyositis (PM) had unusually elevated serum creatine kinase (CK) levels, in a report from the University of Milan, Italy. In patient 1, mother had T cell-mediated PM and CK levels of 2080 U/L at 1 week before cesarean delivery, and >8000 U/L for 3 months after delivery. The infant’s CK was 2000 at birth, 4000 at 45 days, and normal (<185) at 4 months; breast feeding was continued for 2 months. Neurologic exam was normal in the infant, but showed increasing proximal weakness in the mother. Maternal recovery following steroid therapy was accompanied by normal CK levels at 10 months after onset of PM. Patient 2 developed proximal weakness and PM at 6 months in her first pregnancy; her CK levels were 1000-2000 U/L initially and normal after steroid therapy, with recovery by time of delivery. The infant had a normal examination but elevated CK levels (1200 at 10 days, 419 at 1 month, and normal after 2 months). The transplacental passage of maternal autoantibodies to the fetus is considered a possible explanation for the elevated CK in the infants. Chimerism, resulting from the two-way passage of cells between fetal and maternal circulations, is an hypothesis, and transfer of CK during breast feeding is a further possible explanation for the findings. 
COMMENT. Polymyositis during pregnancy is rare and may be associated with stillbirth. In infants who survive, the serum CK may be elevated for extended periods. Normally, CK levels can be increased for 3 to 4 days after birth, especially after vaginal birth.