It also affected the endocrine and immune systems. It was caused by a disruption of neuroelectric impulses during Vulcan mind melds performed by a Vulcan who has been improperly trained. It could be cured by a meld performed by an experienced melder.
The disease and its cure were known in Surak's time, but by the 22nd century the knowledge of the cure had been lost. In that time, melding was considered an "unnatural" practice. As a result, those afflicted with Pa'nar Syndrome were ostracized from Vulcan society. (ENT: "Kir'Shara")
Sub-Commander T'Pol contracted the disease in 2151 when Tolaris initiated a meld with her, although she did not discover this immediately. (ENT: "Fusion") In 2152, Dr. Phlox was able to improve the course of treatment (with the help of Dr. Yuris, who suffered from the disease). (ENT: "Stigma") In 2154, T'Pol was cured by the Syrrannite leader T'Pau, who revealed the true nature of the disease. (ENT: "Kir'Shara")