Conversion isorder is a condition where patients present with neurological symptoms such as numbness, paralysis, or fits, but where no neurological explanation can be found. It is thought that these problems arise in response to difficulties in the patient's life, and conversion is considered a psychiatric disorder in the International Statistical Classification of Diseases and Related Health Problems (ICD-10) and Diagnostic and Statistical Manual of Mental Disorders 4th edition (DSM-IV). Formerly known as 'hysteria', the disorder has arguably been known for millennia, though it came to greatest prominence at the end of the 19th century, when the neurologist Jean-Martin Charcot, and psychiatrists Pierre Janet and Sigmund Freud made it the focus of their study. The term 'conversion' has its origins in Freud's doctrine that anxiety is 'converted' into physical symptoms. Though previously thought to have vanished from the west in the 20th century, new research has suggested it is as common as ever.