Infantile Pyknocytosis Revisited: Possible Familial Trend in a Study of 9 Patients

Infantile pyknocytosis (IP) is an uncommon cause of transient neonatal hemolytic anemia and hyperbilirubinemia occurring in approximately 10% of cases of unexplained neonatal hemolytic anemia.

To study cases of IP with a focus on long-term follow-up, perinatal events, and family history.

Cases were prospectively identified during review of peripheral blood smears for neonatal hyperbilirubinemia during an 11-year period. Clinical and laboratory parameters, follow-up data, and family history were recorded.

Nine cases of IP were identified from the morphologic recognition of pyknocytes and clinical and laboratory evidence of hemolysis, and included 6 males and 3 females. Age at diagnosis ranged from 1 to 18 days (median, 4 days), and gestational age at birth ranged from 29 to 38 weeks (median, 35 weeks). Hemoglobin nadir ranged from 4.9 to 8.1 g/dL (median, 6 g/dL), and maximum total bilirubin concentration ranged from 7.7 to 27.5 mg/dL (median, 22.0 mg/dL). All 9 patients required phototherapy and transfusions. Hemolysis spontaneously resolved without recurrence in all cases, with time to resolution ranging from 13 to 70 days (median, 33 days) and median follow-up of 7 years (range, 1-11 years). Six patients (67%) had a sibling with neonatal jaundice as well. A similar proportion had significant perinatal events.

IP is associated with spontaneous resolution without long-term complications. The underlying etiology is unknown. Perinatal events may expose red blood cells to an overwhelming oxidative stress. Strong family history suggests familial predisposition causing transient red blood cell defect, making them more susceptible to hemolysis.