Conversion disorder (Functional Neurological Symptom Disorder) is categorized under the new Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) category of Somatic Symptom and Related Disorders.  It involves symptoms or deficits affecting voluntary motor or sensory function that suggest a neurologic or other general medical condition. Yet, following a thorough evaluation, which includes a detailed neurologic examination and appropriate laboratory and radiographic diagnostic tests, no neurologic explanation exists for the symptoms, or the examination findings are inconsistent with the complaint. In other words, symptoms of an organic medical disorder or disturbance in normal neurologic functioning exist that are not referable to an organic medical or neurologic cause. 
Common examples of conversion symptoms include blindness, diplopia, paralysis, dystonia, psychogenic nonepileptic seizures (PNES), anesthesia, aphonia, amnesia, dementia, unresponsiveness, swallowing difficulties, motor tics, hallucinations, pseudocyesis and difficulty walking.
Reports of less common manifestations of conversion disorder abound in the literature and include camptocormia, clenched fist syndrome, recumbent gait, odd vocalizations, and pseudo foreign accent syndrome. [3, 4, 5, 6, 7]
Multiple symptoms suggest a somatization disorder. Conversion disorder is a type of somatoform disorder where physical symptoms or signs are present that cannot be explained by a medical condition. Very importantly, unlike factitious disorders and malingering, the symptoms of somatoform disorders are not intentional or under conscious control of the patient. See the image below.
A young woman’s family brings her to the hospital and she presents with a chief complaint of “spells.” It seems that over the past several weeks, the patient has suffered from attacks of bilateral arm jerking, followed by bilateral leg jerking after she lowers herself to the floor. Often, her head shakes violently side to side and her eyes are seen to "roll back in her head" followed by forced eye closure. These incidents follow episodes of emotional outbursts, and the patient is fortunately able to warn others that “I’m about to have a seizure!” After hearing this, her family grabs the patient and places her in a chair or on the ground until the spell is over, which sometimes can wax and wane for 20-30 minutes with varying intensity.
These spells are not accompanied by loss of bladder or bowel continence, but often the patient bites the tip of her tongue and kicks over tables or strikes family members during an episode. This most recent spell occurred while the patient was driving her car, in which she warned of an impending seizure and pulled the car to the shoulder just before losing consciousness; her spell was much more intense than she has had in the past.
She has no significant past medical history and takes no medications. She reports a past history of childhood sexual abuse from a paternal uncle several years ago. On exam, her vitals signs are normal and her neurologic evaluation is without significant findings. She is not orthostatic. Laboratory work-up, including urine toxin screen, is negative.
Conversion symptoms suggest a physical disorder but are the result of psychological factors. According to the psychodynamic model, the symptoms are a consequence of emotional conflict, with the repression of conflict into the unconscious. In the late 1880s, Freud and Breuer suggested that hysterical symptoms resulted from the intrusion of "memories connected to psychical trauma" into the somatic innervation. This mind-to-body process was referred to as conversion. Others have introduced attachment theory as a means to understanding conversion disorder in terms of the freeze response and the appeasement defense behavior seen in animal subjects. 
The patient has been postulated to derive primary and secondary gain. With primary gain, the symptoms allow the patient to express the conflict that has been suppressed unconsciously. With secondary gain, symptoms allow the patient to avoid unpleasant situations or garner support from friends, family, and the medical system that would otherwise be unobtainable. According to sociocultural theories, the direct expression of emotions is impermissible and somatization takes its place. In behavioral models, conversion symptoms are viewed as a learned maladaptive behavior that is reinforced by the environment.
The idea that conversion disorder does not have an organic basis has become entrenched. However, some evidence supports the opposite notion. A review of imaging correlates in patients with motor and sensory conversion symptoms is referenced. [9, 10] Studies on the natural history of conversion disorder indicate that many patients subsequently develop or are found to have preexisting neurologic disease. In fact, conversion disorders may be more frequently observed in patients with a past history of a central nervous system injury. The simultaneous occurrence of organic brain disease with conversion symptoms is also observed, most notably in observation of high rates of organic seizure syndromes associated with psychogenic nonepileptic seizures (PNES). Familial studies have also shown that conversion symptoms in first-degree female relatives are up to 14 times greater than in the general population.
That the diagnosis of a conversion reaction of disorder represents a failed diagnosis of an organic syndrome, perhaps with psychogenic overlay that obscures exam and other findings is usually a valid concern. A recent meta-analysis including more than 1400 cases with follow-up over 5 years reported missed organic diagnosis rates of less than 5%.  This correlates with similar reports for the diagnosis of motor neuron disease or schizophrenia.  Past rates of misdiagnosis were reported as considerably higher. 
Stefansson et al report that the annual incidence of conversion reactions is 22 cases per 100,000 persons per year in Monroe County, New York. However, the reported rates vary widely.  In a study of 100 consecutive women following a normal full-term pregnancy, 33 were noted to have a past history of conversion symptoms. In a study of 100 randomly selected patients from a psychiatry clinic, 24 were noted to have unexplained neurologic symptoms. A report by Carson found that 30% of patients at a neurology clinic had "unexplained symptoms." 
Overall, conversion disorder is reported to be more common in rural populations, in individuals with lower socioeconomic status, lack of education, and low psychological sophistication.  The increased rate of conversion in patients with a past history of sexual or physical abuse is well described. [16, 17]
Stefansson et al report that the annual incidence is 11 cases per 100,000 persons per year in Iceland. 
Individual conversion symptoms are generally self-limiting and do not lead to physical changes or disabilities. In the case of PNES, patients may have driving privileges removed by medical practitioners and may self-limit other activities due to concern over having a paroxysmal event. The symptoms related to the conversion disorder may lead to decreases in quality of life if they are perceived as egodystonic.
Morbidity is often an iatrogenic manifestation of unnecessary diagnostic or therapeutic interventions aimed at establishing an organic diagnosis for the patient's symptoms.
Patients with chronic conversion symptoms rarely may develop atrophy, frozen joints, and contractures from disuse.
Sex- and age-related demographics
Classically, the female-to-male ratio is 2-10:1.
Recent work with PNES reports that males make up approximately 40% of cases. This is a departure from past work, where females made up 80% of cases of PNES in some series. 
Overall, female-to-male ratio is variable, but the occurrence of conversion disorder is likely higher in females overall.
The typical onset is between the second and fourth decades.
The reported range is from children to individuals in their ninth decade of life.