Complex Febrile Seizures As the Initial Presentation of Nutritional Rickets Due to Severe Vitamin D Deficiency

Simple febrile attacks are common in young children and are typically benign. However, complex febrile seizures are characterized by recurrence, focal features, or longer duration and require assessment to determine underlying causes, such as metabolic issues like hypocalcemia. Vitamin D deficiency rickets, a preventable yet re-emerging disease, can also present with seizures. We report a previously healthy, exclusively breastfed eight-month-old boy who developed three episodes of general tonic seizures, initially thought to be triggered by an upper respiratory infection. Further workup revealed hypocalcemia (total calcium of 6.8 mg/dL, ionized calcium of 0.91 mmol/L), severe vitamin D deficiency (25-hydroxyvitamin D of 3.5 ng/mL), low phosphate, elevated alkaline phosphatase, and a high serum parathyroid hormone level, all indicative of nutritional rickets. Other factors that may have contributed to the worsening of his ionized calcium included mild respiratory alkalosis. The patient was treated with IV calcium gluconate, followed by maintenance oral calcium and vitamin D. After the correction of hypocalcemia, he had no further seizures and was discharged. This case underscores the importance of monitoring ionized calcium and vitamin D levels in an exclusively breastfed infant who presents with complex febrile seizures. The sudden decline in ionized calcium, leading to seizures in a susceptible patient, along with fever-induced alkalosis, could be the triggering factors. Prompt diagnosis and appropriate treatment can reduce the risk of neurologic complications from nutritional rickets, thus improving the outcome.