A 3-year-old girl is being evaluated for developmental delay

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A 3-year-old girl is being evaluated for developmental delays. His parents report that the pregnancy was uneventful and that the delivery was without complications. The girl reached all milestones normally during his first year. Length, weight, and head circumference were all well within the normal range during the first year. During her second year, the pediatrician noticed deceleration of head growth, and her parents noticed a gradual decline in her fine motor abilities, frequent hand-wringing movements, and loss of social engagement. Her movements became poorly coordinated. Which of the following is the most likely diagnosis?

A. Asperger disorder
B. Attention-deficit/hyperactivity disorder
C. Autistic disorder
D. Pervasive developmental disorder, not otherwise specified
E. Rett syndrome

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Explanation:
The answer is E. The child described in this case description has the clinical features characteristic of Rett syndrome. During the first five months after birth, the infant has age-appropriate motor skills, head circumference, growth, and social interactions. At six to 30 months, the child has progressive encephalopathy with decline in previously developed motor and social skills. Associated features include seizures in up to 75% of affected children and irregular respiratory patterns. Long-term receptive and expressive communication and socialization abilities remain at a developmental level of less than one year. Rett syndrome occurs almost exclusively in females. Asperger disorder (choice A) is characterized by at least two of the following indications of social impairment: markedly abnormal nonverbal communicative gestures, failure to develop peer relationships, lack of social or emotional reciprocity, and an inability to express pleasure in other people's happiness. Restricted interests and patterns of behavior are also present. Attention deficit/hyperactivity disorder (choice B) is characterized developmentally by an age-inappropriate poor attention span, age-inappropriate features of hyperactivity and impulsivity, or both. Autistic disorder (choice C) is characterized by impairments in social interactions and communication, and restricted repetitive and stereotyped patterns of behavior, interests, and activities. Onset is prior to the age of three years. Pervasive developmental disorder, not otherwise specified (choice D) is a diagnostic category that would be used when a child manifests a qualitative impairment in the development of reciprocal social interaction and communication but does not meet the criteria for other pervasive developmental disorders.