1. Signs and Symptoms

It is common for individuals with PDD-NOS to have more intact social skills and a lower level of intellectual deficit than individuals with other PDDs.^[1] Characteristics of many individuals with PDD-NOS are:

• Communication difficulties (e.g., using and understanding language)^[2]
• Difficulty with social behavior
• Paranoia, a characteristic form of social anxiety, derealization, transient psychosis, and unconventional beliefs if the environment changed without further notice
• Uneven skill development (strengths in some areas and delays in others)
• Unusual play with toys and other objects
• Repetitive body movements or behavior patterns
• Preoccupation with fantasies that interfere and that are not normal to have at a certain age depending on social, cultural and religious norms.
• Unconventional perception of the world
• Maladaptive daydreaming
• Mirrored-Self Misidentification (The delusion that the individual in the mirror is a child, even though they are an older teen or adult)

2. Diagnosis

PDD-NOS is an old diagnostic category. It is not included as an option for an Autism Spectrum Disorder and is not part of the DSM-5, but is included in the ICD-10, as either "atypical autism" or "pervasive developmental disorder, unspecified".^[3]

The diagnosis of a pervasive developmental disorder not otherwise specified is given to individuals with difficulties in the areas of social interaction, communication, and/or stereotypic behavior patterns or interests, but who do not meet the full DSM-4 criteria for autism or another PDD. This does not necessarily mean that PDD-NOS is a milder disability than the other PDDs. It only means that individuals who receive this diagnosis do not meet the diagnostic criteria of the other PDDs, but that there is still a pervasive developmental disorder that affects the individual in the areas of communication, socialization, and behavior.^[1]

As for the other pervasive developmental disorders, the diagnosis of PDD-NOS requires the involvement of a team of specialists. The individual needs to undergo a full diagnostic evaluation, including a thorough medical, social, adaptive, motor skills and communication history.^[1] Other parts of an assessment can be behavioral rating scales, direct behavioral observations, psychological assessment, educational assessment, communication assessment, and occupational assessment.^[4]

Description of PDD-NOS merely as a "subthreshold" category without a more specific case definition poses methodological problems for research regarding the relatively heterogeneous group of people who receive this diagnosis. While it's true that children diagnosed with PDD-NOS, as a whole, show fewer intellectual deficits and are higher-functioning than autistic children, many others who fit the criteria for PDD-NOS have some autistic features but also have intellectual deficits that are so severe that it's difficult or impossible to tell whether some of the deficits come from the autism or from the severe to profound degree of intellectual disability itself. Furthermore, some others who fit the criteria for PDD-NOS come to professional attention at a later age, compared to those diagnosed with autism.^{[5] [6]}

2.1. Subgroups

Studies suggest that persons with PDD-NOS belong to one of three very different subgroups:^[7]

• A high-functioning group (around 25 percent) whose symptoms more or less overlap with that of Asperger syndrome, while also not meeting the criteria for autistic disorder, but who completely differ from those with Asperger syndrome in terms of having a lag in language development and/or mild cognitive impairment.^[7] (The criteria for Asperger syndrome excludes a speech delay or a cognitive delay in early life.^[8])
• Another group (around 25 percent) whose symptoms more closely resemble those of autistic disorder, but do not fully meet all its diagnostic signs and symptoms. This is because either the symptoms were recognized at a later age or because they were too young or have cognitive deficits that are too severe to properly identify all the symptoms of autism that they may have.^[7][9]
• The biggest group (around 50 percent) consists of those who meet all the diagnostic criteria for autistic disorder but whose stereotypical and repetitive behaviors are noticeably mild.^[7]

2.2. Behavior

An association between HFA and criminal behavior is not completely characterized. Several studies have shown that the features associated with HFA may increase the probability of engaging in criminal behavior.^[10] While there is still a great deal of research that needs to be done in this area, recent studies on the correlation between HFA and criminal actions suggest that there is a need to understand the attributes of HFA that may lead to violent behavior. There have been several case studies that link the lack of empathy and social naïveté associated with HFA to criminal actions.^[11]

There is still needs more research on the link between HFA and crimes, because most other studies point out that most people with ASD are ten times more likely to be victims and five times less likely to commit crimes than the general population. But thee are also small-subgroups of people with Low-functioning Autism that commit crimes, because lack of understanding of the laws.

3. Treatment

There is no known "cure" for PDD-NOS, but there are interventions that can have a positive influence. Early and intensive implementation of evidence-based practices and interventions are generally believed to improve outcomes. Most of these are individualised special education strategies rather than medical or pharmaceutical treatment; the best outcomes are achieved when a team approach among supporting individuals is used.

Some of the more common therapies and services include:^[1]

• Visual and environmental supports, visual schedules
• Social stories and comic strip conversations
• Speech therapy
• Physical and occupational therapy^[1]