In 1897 Dr Sigbert Ganser compiled a report about several cases of a previously undescribed psychological condition, in which patients gave approximate answers to questions, had a clouding of consciousness, somatic conversion symptoms and hallucinations - along with impairment of grasp, lack of attention and concentration, and increased anxiety and perplexity.

Initially, it was believed to be rare, occurring mainly in forensic settings. Hence, it was referred to as prison psychosis. Later, such cases were reported more frequently in non-forensic settings. The syndrome has found a place in both the ICD-10 and DSM-IV, despite controversy about its existence and distinctiveness. This disorder was previously classified as a factitious disorder; currently, it is classified under ‘dissociative disorder not otherwise specified’.

Source :Indian J Psychiatry. 2006 Apr-Jun; 48(2): 123–125.

There are currently disputes about the condition's authenticity - some researchers suggest that it's a fake syndrome which is 'acted out' to gain attention. For those who assert that the syndrome is a genuine disorder, there is no explanation as to its cause.

Further info : British Journal of Psychiatry Volume 113, Issue 494, pp. 19-29