Paroxysmal hyperventilation responses in the adult electroencephalogram.

Hyperventilation (HV) is an important activating procedure in clinical EEG. Paroxysmal HV slowing is associated with hypoglycemia and is common in children. Paroxysmal slowing in adults is sometimes interpreted as indicating cerebral instability or paroxysmal tendencies. We investigated the clinical correlates of paroxysmal HV slowing in 100 consecutive EEGs recorded in 1984 and compared these to 100 controls (age-matched normal EEGs recorded since 1982). Twenty-eight percent of patients over 15 with paroxysmal HV slowing not due to hypoglycemia had headaches, 80% of them vascular. Ten percent had syncope, 15% acute behavioral changes possibly representing seizures, 9% psychiatric disorders, 5% assorted complaints of obscure etiology, 20% had clinically definite seizures, 10% assorted neurologic disorders other than epilepsy, and 3% mental retardation. Fewer patients with HV paroxysms had epilepsy than did control individuals (p less than 0.05), while neurologic disorders of other kinds were more often found in those with HV paroxysms (p less than 0.025). Specific psychiatric diagnoses were less frequent in the paroxysmal HV group, but the difference was not significant. Paroxysmal HV responses in non-hypoglycemic adults may identify individuals prone to syncope, vascular headaches, or other autonomic dysfunction. They are not correlated with epilepsy however, and should not be considered abnormal.