Asperger's Disorder is often misdiagnosed as Narcissistic Personality Disorder (NPD), though evident as early as age 3 (while pathological narcissism cannot be safely diagnosed prior to early adolescence).
In both cases, the patient is self-centered and engrossed in a narrow range of interests and activities. Social and occupational interactions are severely hampered and conversational skills (the give and take of verbal intercourse) are primitive. The Asperger's patient body language - eye to eye gaze, body posture, facial expressions - is constricted and artificial, akin to the narcissist's. Nonverbal cues are virtually absent and their interpretation in others lacking.
Yet, the gulf between Asperger's and pathological narcissism is vast.
The narcissist switches between social agility and social impairment voluntarily. His social dysfunctioning is the outcome of conscious haughtiness and the reluctance to invest scarce mental energy in cultivating relationships with inferior and unworthy others. When confronted with potential Sources of Narcissistic Supply, however, the narcissist easily regains his social skills, his charm, and his gregariousness.
Many narcissists reach the highest rungs of their community, church, firm, or voluntary organization. Most of the time, they function flawlessly - though the inevitable blowups and the grating extortion of Narcissistic Supply usually put an end to the narcissist's career and social liaisons.
The Asperger's patient often wants to be accepted socially, to have friends, to marry, to be sexually active, and to sire offspring. He just doesn't have a clue how to go about it. His affect is limited. His initiative - for instance, to share his experiences with nearest and dearest or to engage in foreplay - is thwarted. His ability to divulge his emotions stilted. He is incapable or reciprocating and is largely unaware of the wishes, needs, and feelings of his interlocutors or counterparties.
Inevitably, Asperger's patients are perceived by others to be cold, eccentric, insensitive, indifferent, repulsive, exploitative or emotionally-absent. To avoid the pain of rejection, they confine themselves to solitary activities - but, unlike the schizoid, not by choice. They limit their world to a single topic, hobby, or person and dive in with the greatest, all-consuming intensity, excluding all other matters and everyone else. It is a form of hurt-control and pain regulation.
Thus, while the narcissist avoids pain by excluding, devaluing, and discarding others - the Asperger's patient achieves the same result by withdrawing and by passionately incorporating in his universe only one or two people and one or two subjects of interest. Both narcissists and Asperger's patients are prone to react with depression to perceived slights and injuries - but Asperger's patients are far more at risk of self-harm and suicide.
The use of language is another differentiating factor.
The narcissist is a skilled communicator. He uses language as an instrument to obtain Narcissistic Supply or as a weapon to obliterate his "enemies" and discarded sources with. Cerebral narcissists derive Narcissistic Supply from the consummate use they make of their innate verbosity.
Not so the Asperger's patient. He is equally verbose at times (and taciturn on other occasions) but his topics are few and, thus, tediously repetitive. He is unlikely to obey conversational rules and etiquette (for instance, to let others speak in turn). Nor is the Asperger's patient able to decipher nonverbal cues and gestures or to monitor his own misbehavior on such occasions. Narcissists are similarly inconsiderate - but only towards those who cannot possibly serve as Sources of Narcissistic Supply.