The underlying etiology of infantile spasms (West syndrome): Information from the United Kingdom Infantile Spasms Study (UKISS) on contemporary causes and their classification²

<jats:title>Summary</jats:title><jats:p><jats:bold><jats:styled-content>Purpose:</jats:styled-content> </jats:bold> To examine the underlying etiology of infantile spasms from the United Kingdom Infantile Spasms Study (UKISS), using the pediatric adaptation of ICD 10.</jats:p><jats:p><jats:bold><jats:styled-content>Methods:</jats:styled-content> </jats:bold> Infants were enrolled in a randomized controlled trial or a parallel epidemiologic study. Etiological information included history, examination, and investigations. The infants were classified as <jats:italic>proven etiology,</jats:italic> if a neurologic disease was identified; as <jats:italic>no identified etiology,</jats:italic> if no neurologic disease was identified; and as <jats:italic>not fully investigated,</jats:italic> if a major piece of information was missing. <jats:italic>Proven etiology</jats:italic> was subclassified using the pediatric adaptation of ICD 10. The results were then examined to identify further methods of classification.</jats:p><jats:p><jats:bold><jats:styled-content>Results:</jats:styled-content> </jats:bold> Of 207 infants, 127 (61%) had <jats:italic>proven etiology</jats:italic>, 68 (33%) had <jats:italic>no identified etiology,</jats:italic> and 12 (6%) were <jats:italic>not fully investigated</jats:italic>. Etiologies were prenatal in 63, perinatal in 38, postnatal in 8, and 18 other. The most common etiologies were: hypoxic–ischemic encephalopathy (HIE) 21 (10%), chromosomal 16 (8%), malformations 16 (8%), stroke 16 (8%), tuberous sclerosis complex (TSC) 15 (7%), and periventricular leukomalacia or hemorrhage 11 (5%). The remaining 32 etiologies were all individually uncommon. Response to treatment is given for individual etiologies.</jats:p><jats:p><jats:bold><jats:styled-content>Discussion:</jats:styled-content> </jats:bold> Our method of classification allows the reporting of results by individual diseases, disease groups, or categories and is structured and clear. It avoids the use of poorly defined terms such as <jats:italic>symptomatic</jats:italic> and <jats:italic>cryptogenic</jats:italic>. It can adapt to new neurologic diseases, such as gene defects, and can be used for comparison of different groups of infants, thereby aiding meta‐analysis.</jats:p>