Brainstem dysfunction in Chiari malformation presenting as profound hypoglycemia: Presentation of four cases, review of the literature, and conjecture as to mechanism

OBJECTIVE: We report four patients whose cases resulted in our observation that profound hypoglycemia resulting from intermittent hyperinsulinism play s a significant role in patients with brainstem dysfunction from Chiari I o r II malformations who have intermittent autonomic dysfunction ("blue spell s"). METHODS: The records of four children with severe brainstem dysfunction ass ociated with hindbrain herniation (Chiari I or II malformation) were review ed retrospectively. Each patient had severe lower cranial nerve dysfunction that required tracheotomy and feeding tube placement. After we found that profound hypoglycemia had occurred during a spell of autonomic dysfunction in one patient, the charts of the other three patients were reviewed for ev idence of hypoglycemia. Now, whenever one of them has evidence of autonomic dysfunction, prospective studies of glucose and insulin levels are perform ed. Three of the patients had Chiari II malformation in association with my elomeningocele, and one patient had a Chiari I malformation resulting from Pfeiffer's syndrome. RESULTS: Hypoglycemia occurred in these patients episodically, and usually when their shunts were functioning. The hypoglycemia was associated with hy perinsulinemia in each patient. The brainstem structures of these children (presumably the dorsal motor nuclei of the vagus) were extremely sensitive to changes in local or regional intracranial pressure. These changes were t riggered by intermittent shunt failure, agitation from pain, abdominal dist ention from constipation, and retention of CO,. In patients with Chiari mal formations, even mild increases in intracranial pressure lead to brainstem dysfunction. One possible explanation is that pressure on the deformed Xth cranial nerve nuclei may lead to insulin release and life-threatening hypog lycemia. Continuous-drip feeds are necessary to prevent this complication. CONCLUSION: Patients with severe intermittent brainstem dysfunction after d ecompression of Chiari I or Chiari II malformations should have laboratory studies of glucose levels performed at the time of the episodes to rule out hypoglycemia.