Reply

We would like to thank Drs. Hawley and Payne and Ms. Giannola for their letter in which they describe a “rare complication of hyperventilation” in a patient with glioblastoma multiforme. They describe a patient who developed transient focal neurologic symptoms during hyperventilation. The mechanism of these clinical findings, however, is unclear. Notwithstanding the described focal neurologic symptoms (right hemiparesis and aphasia), the accompanying EEG showed generalized slowing. It is well known that hyperventilation is associated with intermittent focal EEG slowing in patients with mass lesion, and Hawley et al provide an interesting hypothesis as to the cause. They note that hyperventilation may unmask the clinical effects of a focal CNS lesion. They hypothesize that because hyperventilation increased the tumor blood flow, it will produce increased mass effect on the adjacent brain and cause the focal findings. We welcome further investigation into this interesting effect.

An important issue is whether hyperventilation can be performed safely in the presence of brain tumor. Hyperventilation typically precipitates absence (petit mal) seizures with a generalized spike and slow wave discharge (1). It is distinctly uncommon for hyperventilation to precipitate partial (focal) seizures, which is the seizure type associated with intracranial mass lesions (2). Because the individuals in the group we studied had focal brain lesions, it is unlikely that hyperventilation would have triggered partial seizures in this group. The findings described by Hawley were easily reversible when hyperventilation was terminated, and should not cause long-term sequelae.