Creatine kinase brain isoenzyme in infantile osteopetrosis.

A 14-month-old girl with infantile osteopetrosis had hematologic and neurologic complications with severe brain atrophy. Although serum contained high creatine kinase brain isoenzyme activity (CK-BB), CK-BB activity was not detected on repeated cerebrospinal fluid examinations. After frequent blood transfusions and steroid therapy, hematologic involvement improved gradually and disappeared finally at age 11 months; serum CK-BB tended to show a concomitant proportional increase in activity. A 111Indium chloride scan was performed at age 4 weeks when the patient had relatively low serum CK-BB activity. It indicated active extramedullary hematopoiesis in the liver and spleen. The second scan was performed at age 12 months when she had high serum CK-BB activity and indicated active medullary hematopoiesis in the cranium. The tests disclosed that the elevated serum CK-BB activity was the result of bone marrow serum leakage, and not leakage from brain tissue. This finding may be a good marker of medullary hematopoietic activity in patients with osteopetrosis. Meanwhile, biopsied sural nerve revealed storage of cellular debris, including myelin figures in the Schwann cells, which suggested increased degradation process in the cells or lysosomal enzyme deficiency.