Increased serum creatine kinase due to hypocalcemia in vitamin D deficiency

An 8-year-old boy with vitamin D-deficiency rickets, increased serum creatine kinase (CK), and hypocalcemia is described. At 5 years of age, he was evaluated because of recurrent tonic seizures. He had growth retardation, microcephaly, quadriplegia, mental retardation, and epilepsy. Muscle strength was difficult to assess because of multiple joint contractures. Deep tendon reflexes were hyperactive. Laboratory data indicated rachitic changes on x-ray, hypocalcemia, low serum 25-hydroxyvitamin D3 (25-OH-D) and 1-alpha-25-dihydroxyvitamin D3 (1-alpha-25-[OH]2-D) levels, a normal response to the Ellsworth-Howard test, and markedly increased CK. Electromyography and nerve conduction velocities were normal. The patient responded to 1-alpha-OH-D treatment with increased serum calcium and normal CK activity; a significant correlation (p less than 0.01) was observed between calcium and log CK. The clinical course and laboratory findings supported the hypothesis that the increased CK was due to hypocalcemia, which in turn was due to the vitamin D deficiency in the severely handicapped child with malnutrition.