Cough syncope and hyperventilation-induced convulsion in Chiari 1.5 malformation

Chiari malformation type I (CM1) is defined as cerebellar tonsillar herniation below the level of the foramen magnum. Syncope, especially cough syncope, is a rare but important symptom of CM1 patients. Here, we report a CM1 patient, in combination with brainstem herniation (CM1.5), presenting with repetitive syncope who was successfully treated by decompressive surgery. A 43-year-old right-handed male, with 5-year history of repeated episodes of loss of consciousness in association with cough, was investigated. Neurological examination revealed slight muscle weakness, clumsiness, and sensory disturbance in the left upper limb. There was no sign of orthostatic hypotension or orthostatic intolerance. Cranial and spinal magnetic resonance imaging revealed a herniation of the cerebellar tonsils and a syringomyelia. Forced hyperventilation during electroencephalogram (EEG) induced brief generalized symmetric clonic convulsions with preserved consciousness, but no overt EEG seizure patterns or slow activities were found. Based on the diagnosis of CM1.5 with recurrent episodes of loss of consciousness, he underwent foramen magnum decompression. He has no recurrence of the episode after the surgery on 1 year follow-up. Decompressive surgery was an effective procedure for cough syncope and other symptoms of the current patient with CM1.5. Dissociation of cerebrospinal fluid pressure between the cranial and spinal compartments which leads further herniation of the cerebellar tonsils and subsequent compression on the cerebellum and the brainstem is considered to be the major mechanism of his cough syncope. Analysis of EEG can be useful not only to diagnose epileptic seizures but also to elucidate mechanisms of syncope and concurrent involuntary movements.