DIFFERENTIAL DIAGNOSIS OF PDD
| Mental retardation |
| Reactive attachment disorder |
| Language disorders |
| Stereotypic movement disorder |
| Attention-deficit/hyperactivity disorder |
| Social phobia |
| Obsessive-compulsive disorder |
| Selective mutism |
| Schizophrenia |
| Personality disorders |
| Normality |
Other symptoms that are relatively specific to autism and PDD include lack of appropriate eye-to-eye gaze, abnormal speech prosody, echolalia, pronominal reversal, and narrow and circumscribed interests. The presence of these symptoms in excess should increase your suspicion of comorbid PDD.
RAD Reactive attachment disorder presents with abnormal social relatedness that can sometimes be confused with milder PDDs, especially in patients with comorbid mental retardation. In RAD, however, a history of severe neglect or abuse is thought to have caused the abnormal social relatedness. Placing the child in a caring and secure environment should improve many of the social deficits.
Language disorders are distinguished from PDDs by the absence of marked social impairment and lack of restricted interests and repetitive behaviors. In addition, children with primary language disorders often have intact nonverbal communication skills and make other attempts to communicate (e.g., through gesture, eye contact).
Stereotypic movement disorder can be seen in individuals with and without comorbid mental retardation. It is not diagnosed in the presence of autism, as these movements are thought to be part of the underlying disorder. The lack of social and communication impairments distinguishes stereotypic movement disorder from PDD.
ADHD Many children with autism and other PDDs have interfering symptoms of inattention, hyperactivity, and impulsivity. We usually do not give them an additional diagnosis of ADHD, as these symptoms are common in PDD. The pathophysiology of these symptoms may be different in ADHD and PDD, as evidenced by the frequent report of adverse effects following stimulant treatment of children with autism.2
Social phobia In higher functioning individuals with PDD, excessive social anxiety can sometimes be confused with social phobia. In social phobia, however, individuals usually do not exhibit marked problems with social relatedness and are able to interact normally with persons they know well and in some situations.
OCD Obsessive-compulsive disorder can occur in individuals with PDD but must be distinguished from the abnormal preoccupations and ritualistic behavior characteristic of autism. In autism, these activities often differ in quality from obsessions and compulsions.3 Furthermore, they usually are not associated with distress, and repetitive behaviors are not linked to a specific obsession.
Selective mutism is usually easy to distinguish from PDD because the affected child is typically able to talk in certain environments, such as at home. Also, the onset of selective mutism follows a period of normal social and communicative development.
Schizophrenia Autism was historically conceptualized as a type of childhood schizophrenia but is now thought to be distinct from the psychotic disorders. Schizophrenia with onset in childhood is much more rare than autism. Its onset usually occurs after several years of normal development, though some children with schizophrenia may have symptoms that resemble PDD early in their illness.4 Autistic persons may at times present with symptoms of a thought disorder. A diagnosis of schizophrenia usually is not made without evidence of prominent delusions and hallucinations.
Personality disorders PDDs are sometimes difficult to distinguish from personality disorders with similar features (e.g., schizotypal personality, schizoid personality). The social impairment in autistic and Asperger’s disorders is generally of earlier onset and greater severity than that seen in personality disorders. Those with personality disorders also typically lack stereotyped language or repetitive behaviors that are common in PDDs.
Table 4
CHARACTERISTIC FEATURES OF DSM-IV SUBTYPES OF PERVASIVE DEVELOPMENTAL DISORDERS
| Feature | Autistic disorder | Asperger’s disorder | Rett’s disorder | Childhood disintegrative disorder | Pervasive developmental disorder NOS* |
|---|---|---|---|---|---|
| Sex | Male:female ratio 4:1 | Male > female | Females only | Male > female | Male > female |
| Age of onset | < 3 years | Variable | 5-30 months | 2-10 years | Variable |
| Presence of regression | Mild regression in minority of patients | No | Yes | Yes | No |
| IQ | Most have mental retardation | Most have normal intellectual functioning | Severe mental retardation | Severe mental retardation | Variable |
| Social impairment | Yes | Yes | Yes | Yes | Yes |
| Communication impairment | Yes | No | Yes | Yes | Variable |
| Restricted interests/repetitive behaviors | Yes | Yes | Yes | Yes | Variable |
| Motor involvement | Usually not | Some have motor clumsiness | Gait and trunk ataxia; loss of purposeful hand movements | Loss of bowel/bladder control | Variable |
| *NOS: Not otherwise specified | |||||
Social awkwardness Finally, some of the PDDs that allow higher functioning (e.g., Asperger’s disorder and PDD not otherwise specified [NOS]) need to be distinguished from normal social awkwardness that can be common, especially in adolescence. The social impairment in PDD is marked and interferes with normal functioning and development.
Step 3. Which PDD is it?
DSM-IV describes five subtypes of PDD (autistic disorder, Asperger’s disorder, Rett’s disorder, childhood disintegrative disorder, and PDD NOS) that have in common problems with reciprocal social interaction (Table 4). For psychiatrists making the diagnosis, it is probably most difficult to differentiate the two most common types: autistic and Asperger’s disorders.
Autistic disorder is the prototypical PDD that is associated with abnormalities in reciprocal social interaction, qualitative impairments in communication, and narrow interests and repetitive behaviors (Table 1). By definition, symptoms of the disorder manifest by age 3.