Individuals with Autistic Disorder may have a range of behavioral symptoms, including hyperactivity, short attention span, impulsitivity, aggressiveness, self-injurious behaviors, and, particularly in young children, temper tantrums.   There may be odd responses to sensory stimuli (e.g.,a high threshold for pain, oversensitivity to sounds or being touched, exaggerated reactions to light or odors, fascination with certain stimuli).   There may be abnormalities in eating (e.g.,limiting diet to a few foods, Pica) or sleeping (e.g.,recurrent awakening at night with rocking).   Abnormalities of mood or affect (e.g.,giggling or weeping for no apparent reason, an apparent absence of emotional reaction) may be present.   There may be a lack of fear in response to real dangers, and excessive fearfulness in response to harmless objects.   A variety of self-injurious behaviors may be present (e.g.,head banging or finger,hand, or wrist biting).   In adolescence or early adult life, individuals with Autistic Disorder who have the intellectual capacity for insight may become depressed in response to the realization of their serious impairment.

      When Autistic Disorder is associated with a general medical condition, laboratory findings consistent with the general medical condition will be observed.   There are group differences in some measures of serotonergic activity, but these are not diagnostic for Autistic Disorder.   Imaging studies may be abnormal in some cases, but no specific pattern has been clearly identified.   EEG abnormalities are common even in the absence of seizure disorders.

      Various nonspecific neurological symptoms or signs may be noted (e.g.,primitive reflexes, delayed development of hand dominance) in Autistic Disorder.   The condition is sometimes observed in association with a neurological or other general medical condition (e.g.,fragile X syndrome and tuberous sclerosis).

      Seizures may develop (particularly in adolescence) in as many as 25% of cases.   Both microcephaly and macrocephaly are observed.   When other general medical conditions are present, they should be noted on Axis III.

      The nature of the impairment in social interaction may change over time in Autistic Disorder and my vary depending on the developmental level of the individual.   In infants, there may be a failure to cuddle; an indifference or aversion to affection or physical contact; a lack of eye contact, facial responsiveness, or socially directed smiles; and a failure to respond to their parents' voices.   As a result, parents may be concerned initially that the child is deaf.   Young children with this disorder may treat adults as interchangeable, may cling mechanically to a specific person, or may use the parent's hand to obtain desired objects without ever making eye contact (as if it were the hand rather than the person that is relevant).   Over the course of development, the child may become more willing to be passively engaged in social interaction and may even become more interested in social interaction.   However, even in such instances, the child tends to treat other people in unusual ways (e.g.,expecting other people to answer ritualized questions in specific ways, having little sense of other people's boundaries, and being inappropriately intrusive in social interaction).   In older individuals, tasks involving long-term memory (e.g.,train timetables, historical dates, chemical formulas, or recall the exact words of songs heard years before) may be excellent, but the information tends to be repeated over and over again, regardless of the appropriateness of the information to the social context.   Rates of the disorder are four to five times higher in males than in females.   Females with the disorder are more likely, however, to exhibit more severe Mental Retardation.

      Periods of developmental regression may be observed in normal development, but these are neither as severe or as prolonged as in Autistic Disorder.   Autistic Disorder must be differentiated from other Pervasive Developmental Disorders.   Rett's Disorder differs from Autistic Disorder in its characteristic sex ratio and pattern of deficits.   Rett's Disorder has been diagnosed only in females, whereas Autistic Disorder occurs much more frequently in males.   In Rett's Disorder, there is a characteristic pattern of head growth deceleration, loss of previously acquired purposeful hand skills and the appearance of poorly coordinated gait or trunk movements.   Particularly during the preschool years, individuals with Rett's Disorder may exhibit difficulties in social interaction similar to those observed in Autistic Disorder, but these tend to be transient.   Autistic Disorder differs from Childhood Disintegrative Disorder, which has a distinctive pattern of severe developmental regression in multiple areas of functioning following at least 2 years of normal development.   In Autistic Disorder, developmental abnormalities are usually noted within the first year of life.   When information on early development is unavailable or when it is not possible to document the required period of normal development, the diagnosis of Autistic Disorder should be made.   Asperger's Disorder can be distinguished from Autistic Disorder by the lack of delay or deviance in early language development.   Asperger's Disorder is not diagnosed if criteria are met for Autistic Disorder.

      Schizophrenia with childhood onset usually develops after years of normal, or near normal, development.   An additional diagnosis of Schizophrenia can be made if an individual with Autistic Disorder develops the characteristic features of Schizophrenia with active-phase symptoms of prominent delusions or hallucinations that last for at least 1 month.   In Selective Mutism, teh child usually exhibits appropriate communication skills in certain contexts and does not have the severe impairment in social interaction and the restricted patterns of behavior associated with Autistic Disorder.   In Expressive Language Disorder and Mixed Receptive-Expressive Language Disorder, there is a language impairment, but it is not associated with the presence of a qualitative impairment in social interaction and restricted, repetitive, and stereotyped patterns of behavior.   It is sometimes difficult to determine whether an additional diagnosis of Autistic Disorder is reserved for those situations in which there are qualitative deficits in social and communicative skills and the specific behaviors characteristic of Autistic Disorder are present.   Motor stereotypies are characteristic of Autistic Disorder; an additional diagnosis of Stereotypic Movement Disorder is not given when these are better accounted for as part of the presentation of Autistic Disorder.   Symptoms of overactivity and inattention are frequent in Autistic Disorder, but a diagnosis of Attention-Deficit/Hyperactivity Disorder is not made if Autistic Disorder is present.