It is only since the late 1800s that narcissism has been defined in psychological terms:
Havelock Ellis (1898) was the first psychologist to use the term when he linked the myth to the condition in one of his patients. Sigmund Freud (1905-1953) used the terms "narcissistic libido" in his Three Essays on the Theory of Sexuality. Ernest Jones (1913/1951) was the first to construe extreme narcissism as a character flaw. Robert Waelder (1925) published the first case study of narcissism. His patient was a successful scientist with an attitude of superiority, an obsession with fostering self-respect, and a lack of normal feelings of guilt. The patient was aloof and independent from others and had an inability to empathize with others situations, and was selfish sexuality. Waelders patient was also overly logical and analytical and valued abstract intellectual thought (thinking for thinkings sake) over the practical application of scientific knowledge.Narcissistic personality was first described by the psychoanalyst Robert Waelder in 1925. The term narcissistic personality disorder (NPD) was coined by Heinz Kohut in 1968. Waelders initial study has been influential in the way narcissism and the clinical disorder Narcissistic personality disorder are defined today

Freudianism and psychoanalysis
Much early history of narcissism and NPD originates from psychoanalysis. Regarding the adult neurotics sense of omnipotence, Sigmund Freud said that "this belief is a frank acknowledgement of a relic of the old megalomania of infancy"; and concluded that: "we can detect an element of megalomania in most other forms of paranoic disorder.
Assessment and screening
Narcissistic Personality Inventory
Risk factors for NPD and grandiose/overt and vulnerable/covert subtypes are measured using the narcissistic personality inventory, an assessment tool originally developed in 1979, has undergone multiple iterations with new versions in 1984, 2006 and 2014. The subtype is also assessed with the pathological narcissism inventory (PNI). The PNI is a screening tool for antisocial, borderline, narcissistic personality disorders. The PNI scales exhibited significant associations with parasuicidal behavior, suicide attempts, homicidal ideation, and several aspects of psychotherapy utilization. Pathological narcissism a term for concurrent grandiose and vulnerable narcissism, which is linked to poor self-esteem, lack of empathy, feelings of shame, interpersonal distress, aggression, and significant impairments in personality functioning across both clinical and non-clinical samples. Despite the phenomenological and empirical distinction between vulnerable and grandiose narcissism, some theories suggest that grandiose narcissists also have fragile personality traits. There are a number of other assessment tools for narcissism and NPD subtypes. Millon Clinical Multiaxial Inventory
The Millon Clinical Multiaxial Inventory (MCMI) is another diagnostic test developed by Theodore Millon. The MCMI includes a scale for narcissism. The NPI and MCMI have been found to be well correlated. Whereas the MCMI measures narcissistic personality disorder (NPD), the NPI measures narcissism as it occurs in the general population; the MCMI is a screening tool. In other words, the NPI measures "normal" narcissism; i.e., most people who score very high on the NPI do not have NPD.