This chapter describes the magnitude of the problem of mental illness, both globally and in terms of specific mental health-related visits encountered in emergency department (ED) settings. The WHO's cross-national comparisons show a globally high prevalence of major Diagnostic and Statistical Manual of Mental Disorders, 4th Edition (DSM-IV) mental disorders (anxiety disorders, mood disorders, impulse control disorders, substance use disorders) with 25th-75th percentiles ranging from 18.1% to 36.1%. The chapter describes the magnitude of the problem of ED presentations for specific mental disorders. The most prevalent conditions are highlighted. After anxiety disorders, mood disorders are the second most common psychiatric disorder in the general population, occurring in 10% of the U.S. adult population each year. Schizophrenia spectrum diagnoses account for approximately two thirds of all psychotic disorders. Almost 1 in 10 of the adult U.S. population is estimated to have an Axis II personality disorder in any year.

Psychogenic nonepileptic seizures (PNES) are paroxysms of altered bodily/mental function. Careful history-taking can elicit most risk factors for PNES. Comorbid psychiatric diagnoses including depression, anxiety, and personality disorder, and family history of psychiatric disorders are also PNES risk factors. Seizure semiology is crucial for raising the clinician's suspicion of PNES, and is often the first step towards making the correct diagnosis. Most studies that assess seizure semiology are structured as retrospective analyses of long-term video EEG. Various prognostic indicators have been reported including clinical and psychological factors. Poorer prognosis is associated with the presence of chronic depression, an Axis II personality disorder, and a history of abuse or trauma. Clinical experience and prior-published treatment reports reveal that coordination between neurologists and psychiatrists/psychologists, with accurate diagnosis and prompt initiation of psychotherapy and communication between care providers, patient and family, yields higher treatment success.