37 yr old woman c/o no sweating at all. In day light claims of shooting temperature to intolerable degrees that she has to dwell to an a/c room to cool her down. In o/p, no sweating seen and always skin and oral temperature >99'F. Not a congenital one but acquired in middle (2-3 years back).

Basic blood investigations, thyroid and other vitals normal. Seems to be mildly depressed. What could be the diagnosis and how to proceed with investigations and treatment?