Hyperventilation-induced cerebellar fit in a patient with Chiari 1.5 malformation

Cerebellar fit (CF) is characterized by paroxysmal head retroflexion and opisthotonus with preserved consciousness.^1-3 Here, we present a case of a 43-year-old male with cough syncope (CS) due to Chiari 1.5 malformation, who exhibited CF during hyperventilation (HV).⁴ EEG revealed a normal posterior dominant rhythm of 8–9 Hz. Approximately 150 s after initiating HV, the patient experienced truncal convulsion accompanied by opisthotonic posturing (Video 1). Notably, the patient retained his consciousness with open eyes. No electrographic seizure patterns were evident, the posterior dominant rhythm was preserved, and the electrocardiogram demonstrated normal sinus rhythm (Figure 1). He underwent a foramen magnum decompression and his CS and CF disappeared. As a mechanism, HV may induce dissociation between intracranial and spinal cord cerebrospinal fluid pressures, which further lower the cerebellum and compress the brainstem and cerebellum.^2-5 CF may be caused by the Guillain–Mollaret triangle disruption and CS by dysfunction of the brainstem reticular formation.^{6, 7}

This study was partially supported by JPJSBP 120217720 and by the Nakatani Foundation for Advancement of Measuring Technologies in Biomedical Engineering : Technology Exchange Program.

None of the authors have any conflicts of interest to declare.