Transient Axial Hypotonia and Alteration of Consciousness in an Infant With Chiari I Malformation

Abstract

This is an 11-months-old girl, who presented to a pediatric neurologist with episodes of “becoming limp with eye deviation to the left and falling backwards while awake.” The first episode occurred 3 weeks before presentation as an isolated event, rapidly became frequent, occurring multiple times a day. The past medical history and development were normal except for mild gross motor delay, as the infant was not sitting unsupported at 10 months. The examination showed mild symmetric hypotonia with normal reflexes. Family history was unremarkable regarding neurological disorders. Magnetic resonance imaging (MRI) of the brain revealed Chiari I malformation with an abnormal T2 signal within the cervical cord, consistent with possible syringomyelia. Electroencephalogram (EEG) showed the presence of spikes in the left temporal region. During the EEG, a typical episode occurred, associated with diffuse delta activity. Because the nature of the events was unclear, and because of the potential need for surgical intervention, the infant was referred for further evaluation. Table 1 summarizes the diagnostic work-up in the hospital. Repeat MRI of the brain and spine, with and without gadolinium, confirmed Chiari I malformation, in which cerebellar tonsils extended approximately 1.5 cm below the foramen magnum. MRI of the cervical spine revealed focal expansion of the spinal cord at C2-C3 level with associated T2 signal changes (Fig 1). The degree of tonsillar ectopia with an abnormal T2 signal within the cervical spinal cord coupled with the developmental motor delay prompted a neurosurgical recommendation of decompressive craniotomy. Additionally, there was the clinical suspicion that the events of axial hypotonia may be caused by transient increases in intracranial pressure due to Chiari I malformation. Several target events were captured on video-EEG during the 7-day admission. Most of these events occurred while the infant was sitting. The infant would start responding poorly to the mother’s voice as well as ignoring the toys presented to her, then sway from side to side and become limp, followed by falling on her back with preserved bilateral finger and feet movements. The events lasted approximately 3 minutes, with a slow return to previous activities. There were no associated changes in respiration or cardiac patterns. Neurological examination showed that the infant was not responsive to verbal and visual stimulation, and there was proximal hypotonia