Ganser syndrome, as it is now known, has been the subject of much debate since this original paper. Questions about its etiology, definition, and classification, as well as its status as a true mental illness versus a specific form of malingering has been the subject of multiple journal articles and book chapters. The syndrome is not listed in the Diagnostic and Statistical Manual of Mental Disorders,Fifth Edition (DSM-5) as it had been in previous editions.
In 1898, German psychiatrist Sigbert Ganser first published a lecture, delivered the previous year, describing 3 patients who exhibited a set of symptoms that he felt described a new hysterical syndrome. He began the lecture with an extract of the following conversation he had with one of these patients (as translated from German by C.E. Shorer).
Q. Are you able to count to ten?
A. Yes (But he does not, and is silent.)
Q. Well, then, count.
A. (But he does not, and only counts on being prompted.) 1, 2, 3, 4. (Then he is quiet again.)
Q. What follows 1?
A. 12, 93 and . . .
Q. And after 93?
A. (He continues in that fashion.)
(On another occasion)
Q. How much are 2 and 1?
Q. 3 and 2?
Q. 5 and 2?
Q. What is 4 minus 1?
A. 5 (Then he corrected the answer to 3.)
Q. In what city are we?
A. In Berlin, in Russia.
Q, What are you doing here?
A. We wanted to go hunting, and we unhitched our horses.
Q. How many noses do you have?
A. I don't know
Q. Have you any nose at all?
A. I do not know if I have a nose.
Q. Have you eyes?
A. I have no eyes.
Q. How many fingers do you have?
Q. How many ears?
A. (He first touches his ears, and then says: 2.)
Q. How many legs does a horse have?
Q. An elephant?
Q. After being shown a coin and asked, What is that?
A. A map which a person hangs on his watch chain. Glancing at the eagle stamped upon a coin: I don't know that person. Is it Kaiser Wilhelm?
Q. He was shown a dollar and was asked: Do you know a dollar?
A. I don't know a dollar. That is a toy which one gives to children.
Q. What is your name?
A. My name is Furst. (Incorrect)
The most well-recognized symptom of Ganser syndrome is the so-called symptom of approximate answers (alternately designated in the literature by the German terms vorbeireden [talking past], vorbeigehen [to pass by], or danebenreden [talking next to]). Here, the patient responds to questions with an incorrect answer, but by the nature of the answer reveals an understanding of the question posed. This can be illustrated by the patient answering "3" when asked, "How many legs has a horse?" or "black" when asked "What color is snow?" or "Tuesday" when asked "What is the day after Sunday?" Frequently, the patient answers a number of questions with these odd approximate answers. This is in direct contrast to answers that are simply nonsensical, perseverative, or otherwise inappropriate.
Although approximate answers may be the most obvious of the symptoms, Ganser was clear that the syndrome included other important components. In all 3 of his patients he observed a time-limited condition that involved a clouding of consciousness that resolved rather suddenly, leaving only a residual amnesia for the events occurring while symptomatic. He referred to this as a "hysterical twilight state." He also described hallucinations in all 3 patients (which he assumed to be present from their behavior, not from patient complaints), as well as so-called hysterical stigmata. By this last statement, Ganser is referring to symptoms we would today associate with a conversion disorder. Ganser found sensory changes involving decreased reactivity to pinprick in all 3 patients, and in 1 patient he found the areas that were hyperalgesic to change depending on the day. He further described another case in the literature where the patient displayed "intractable paralysis and sensory disturbances."
In this initial paper, Ganser identified case reports published earlier by both Neisser and Dietz, where patients with similar symptoms were assumed to be malingering and strongly argued against this interpretation. He pointed to the change in consciousness as well as the conversion symptoms as proof that this was a hysterical syndrome and not simple malingering. By hysteria here, Ganser is referring to a broad concept that would encompass many of the diagnoses list in the DSM under both somatoform disorders and dissociative disorders.
Shortly after the publication of his findings, a healthy debate ensued. Aside from the expected protestations that the patients were really malingering and Ganser was being duped, others made the argument that these symptoms were not hysterical, but instead manifestations of other psychiatric conditions. Ganser's mentor, Franz Nissl, believed it to be a manifestation of catatonic negativism, and in fact 1 of Ganser's 3 patients did in fact have catatonic posturing as a feature of his condition. A 1904 report by Vorster argued that he found Ganser's symptoms occurred in as many as 21% of catatonic patients observed. Ganser replied to these challenges by postulating that his symptoms revealed a hysterical condition within catatonia.
Others described other conditions where this syndrome may exist. In 1904, Henneberg reported on patients with these symptoms in mania, depression, and schizophrenia, as well as in otherwise healthy people who were drunk or who were intentionally giving "foolish answers to foolish questions." Ruggles reports several other unnamed observers who described this condition in mental retardation and dementia, as well as manic patients attempting to voluntarily make jokes.  Since that time, Ganser symptoms have been described in numerous states including neurosyphilis, epilepsy, poststroke, meningiomas, postanoxia, postpartum psychosis, traumatic brain injuries, infections, and various dementias.
In Ganser's time as well as today, the difficulty in interpreting much of this literature is the nebulous criteria used to define the syndrome. In Ganser's 3 patients, he notes that all 3 were prisoners and all 3 had previous medical conditions believed to precipitate their symptoms (2 had suffered a head injury with loss of consciousness and the third had just suffered from a severe episode of typhus). He notes that all 3 suffered from hallucinations, decreased response to pinprick and a "clouding of consciousness" in addition to their tendency to provide approximate answers to questions, and all 3 had a spontaneous resolution of their symptoms with amnesia for events occurring during the episode.
Although Ganser is clear that he does not feel approximate answers is enough to make a diagnosis, many later papers rely on this single symptom as the basis of their case reports and have done little but prove that this symptom lacks specificity when used alone. However, when we attempt to expand our definition to include other symptoms described by Ganser, we are left with the dilemma of determining what is necessary and what is optional.
In an attempt to deal with this problem Enoch and Trethowan proposed a set of 4 criteria based on their interpretation of Ganser's work: approximate answers, clouding of consciousness, hallucinations (visual and auditory), and somatic conversion symptoms.  Curiously, other aspects of Ganser's description, including, limited time-course, sudden remission, and amnesia for events during the illness are not specified in their criteria. Although the formulation of these criteria have been valuable in educating people in the field, their use as a tool has been somewhat limited due to the unclear nature of which criteria are necessary for the diagnosis, and the neglect of certain features, such as the transient nature of the illness, that Ganser appeared to believe was central to the presentation.
The basic underlying etiology of Ganser syndrome is unknown. From the time of the earliest case reports, debates over the factitious versus psychiatric versus organic origin of the symptomatology were common in the literature. These causative explanations are not mutually exclusive, and all patients may not develop this set of symptoms for the same reasons.
Organic etiologies have been proposed due to the obvious comparisons with acute delirium, as well as the frequent history of head injury or recent illness in these patients. In Ganser's 3 original patients, 1 had just suffered through a particularly severe episode of typhus while the other 2 had experienced significant head injuries in the past. Since that time, researchers have found patients where organic etiologies such as head injury, dementia (specifically frontotemporal dementia and Huntington), alcoholism, epilepsy, stroke, and cerebral infection, appeared instrumental in the manifestation of the syndrome. Of particular note, a positron emission tomography (PET) study was performed on a single patient exhibiting the syndrome after suffering severe, asthma-induced hypoxia. The study revealed hypometabolism in the bilateral occipital and posterior temporal and parietal lobes. 
Various psychiatric explanations have also been proposed to explain this syndrome. A commonly suggested psychodynamic mechanism for the syndrome is the urge to avoid an unpleasant situation and its burden of responsibility. Some pointed to the limited time-course of the syndrome as well as the subsequent amnesia and championed the idea that it is a particular type of dissociative disorder. Others found symptoms in patients diagnosed with schizophrenia or catatonia and emphasized the psychotic or catatonic nature of the syndrome.
Malingering and factitious disorder have also proposed as possible etiologies, particularly since Ganser's original observations were described in prisoners. The literature contains a number of case reports of patients believed to be consciously or unconsciously producing their symptoms for secondary gain, though the author is aware of only one report where other objective evidence of malingering was offered. 
Some of the confusion surrounding the etiology and pathophysiology of Ganser syndrome is likely related to the varying definitions used to diagnose the disorder. Although Ganser was very specific that he was talking about a syndrome that included more then just approximate answers, rarely are these stringent diagnostic criteria actually used.
The full Ganser syndrome is considered very rare. Fewer than 100 cases have been described and documented in the literature.
Symptoms usually resolve spontaneously. Occasionally, they may be followed by a major depressive episode.
Mortality and morbidity may be associated with the underlying etiology, especially if organic.
Amnesia for events that occurred during the episode is common.
Information on race has not always been available in the case reports, but patients of all racial origins have been reported. Some have noted that it may be more frequent in those of a racial minority status.
In one review of 43 case reports, 74% were noted to be male. In another review of 15 case reports, all were male. The vast majority of case reports are male, but whether this difference is real or due to selection bias is uncertain.
In one review of 43 case reports, the average age was 32 years, with a range from 15-62 years. Cases from across the age range have been reported.