The evolution of cerebral arteriopathy in 50 children with first arterial ischemic stroke (AIS) was evaluated at Great Ormond Street Hospital for Children, and Neuroscience Unit, Institute of Child Health, London. The median age was 49 months (range 4 mo to 14 yr). Risk factors for AIS included varicella-zoster within 12 months (22 patients), congenital heart disease (4), sickle cell disease 1, and gene mutations in 6. Arteriopathy graded for severity on serial MR angiograms affected 72 arteries in 43 (86%) patients; 5 had clinical recurrence, 12 were progressive, 24 improved, and 7 were stable. Magnetic resonance angiograms were normal in 7. Arteriopathy was transient in 24, chronic in 11, and diagnoses included arterial dissection in 3, moyamoya (3), and vasculitis in 1. In patients with progressive arteriopathy, the hazard of stroke recurrence was increased threefold. After adjusting for age and AIS risk factors, the hazard ratio was 3.1; p=0.27). 
COMMENT. The authors have employed serial magnetic resonance angiography to distinguish a relatively benign and self-limiting vasculopathy from progressive types such as moyamoya. Risk factors that determine progression of arteriopathies include a history of varicella zoster, congenital heart anomalies, immunodeficiences, and hemolytic anemias, especially sickle cell disease. In addition to varicella, enteroviruses and Borrelia are reported as triggers for arterial ischemic stroke. [2, 3]
EEG hyperventilation in sickle cell disease is a preventable risk factor for arterial stroke, not mentioned by the above authors. Three reports and four childhood cases of sickle cell disease (SCD) with stroke precipitated by routine hyperventilation during EEG recordings are cited in the literature. The earliest report  concerned an 11-year-old girl with SCD who developed a left hemiparesis immediately following hyperventilation during an EEG. Recovery was incomplete in all cases. Additional cases have involved hyperventilation secondary to obstructive sleep apnea, or ingestion of toxic doses of aspirin. Hyperventilation-induced hypocapnea leads to arterial constriction, decreased cerebral blood flow, and in patients with SCD, intravascular sickling precipitated by hypoxia and cerebral ischemia or infarction. Seizures occurring in 12-14% of patients with SCD are a precursor to stroke in 10-33% and may be associated with vasculopathy, focal hypoperfusion, and silent infarction . The lack of appreciation of potential dangers of hyperventilation in SCD in some reports prompted a cautionary comment and review of the literature (Millichap JG. Clin EEG and Neuroscience, in press) . The avoidance of hyperventilation in patients with SCD is recommended.