A 9-week-old, full-term female infant presented to the hospital with new onset fevers, irritability, and tachycardia. Her temperature was 38.9 degrees Celsius, heart rate 180 beats per minute, respiratory rate 32 breaths per minute, and blood pressure 111/76 mmHg. Her weight was in the third percentile (4010 g), and her height was in the second percentile (52.8 cm). On exam, she was well-proportioned, nondysmorphic without hepatosplenomegaly. She had a full head of hair with no obvious skeletal or skin abnormalities.
Her CBC showed total white blood cell count 4.3 x109/L, absolute neutrophil count 0.09 x109/L, absolute lymphocyte count 3.5 x109/L, Hg 6.7 g/dL, reticulocyte count 1.4%, MCV 96.5 fL, and platelets 231 x109/L.
A review of her peripheral blood smear was remarkable only for a paucity of neutrophils but showed normal morphology in all cell lines. Her electrolyte panel and hepatic function tests, including a bilirubin, bicarbonate, albumin, and LDH were normal. Due to persistent tachycardia and irritability, she received a packed red blood cell transfusion. A “rule out sepsis” evaluation was not revealing, with negative blood, urine, and CSF cultures. It was felt that her clinical presentation and cytopenias were due to a viral illness.
After recovery from her febrile illness, she was discharged home with outpatient hematology follow-up. All of her cells lines normalized except for her absolute neutrophil count, which at various times ranged from 40 to 1200.
She continued to have failure to thrive, with length significantly below the 3rd percentile. Her only gastrointestinal complaint was occasional constipation.
An abdominal ultrasound showed normal kidneys, confirmed no hepatosplenomegaly, but did reveal pancreatic atrophy with findings suggestive of fat replacement. A chromosome breakage study with diepoxybutane was normal.