This is a very good question. It's true that there might be some problems to differentiate Asperger's Syndrome and Schizoid Personality Disorder, infact, according to DSM-5
Individuals with a Schizoid Personality Disorder shows a pattern of dethachment from social
relationships and a restricted range of emotional expression.
Moreover, the manual specifies the likeness of symptoms between Schizoid Personality Disorder and Autism Spectrum Disorder but the latter records
a more severely impaired social interaction and stereotyped behaviors and interests.
According to DSM-5, A personality disorder is an enduring pattern
of inner experience and behavior that deviates markedly from the expectations of the individual's
culture, is pervasive and inflexible and occur in two or more of these fields: 1- cognition 2- affectivity 3- interpersonal functioning 4- impulse control
The DSM-5 divided Personality disorders in three Clusters:
- Cluster A includes paranoid, schizoid, and schizotypal personality disorders.
- Cluster B includes antisocial, borderline, histrionic,
and narcissistic personality disorders,
- Cluster C includes avoidant, dependent, and obsessivecompulsive
Cluster A refers to "Individuals with
these disorders often appear odd or eccentric." They show a bizzarre and strange behavior.
The cognitive and perceptive dimension - dysfunctional in that disorders - has been correlated with an increased activity of dopaminergic system (Siever, Davis, 2004)
With regards to Aperger's Syndrome, DSM-5 folded it into the umbrella of autism spectrum disorders.
To the diagnose is needed:
- Persistent deficits in social communication and social interaction across multiple contexts
- estricted, repetitive patterns of behavior, interests, or activities, as manifested by at least two of the following, currently or by history
- Symptoms must be present in the early developmental period (Not essential for a diagnose of Schizoid Personality Disorder)
- Symptoms cause clinically significant impairment in social, occupational, or other important areas of current functioning
- These disturbances are not better explained by intellectual disability
DSM-5 diagnostic criteria of Autism Spectrum Disorder
DSM - 5 (2013)
Siever LJ1, Davis KL. The pathophysiology of schizophrenia disorders: perspectives from the spectrum