paresis, , psychosis caused by widespread destruction of brain tissue occurring in some cases of late syphilis. Mental changes include gradual deterioration of personality, impaired concentration and judgment, delusions, loss of memory, disorientation, and apathy or violent rages. Convulsions are not uncommon, and while temporary remissions sometimes occur, untreated paresis is eventually fatal.
Paresis occurs most frequently in men between 35 and 50 years of age. The malarial treatment of paresis, effective because the malarial fever destroys the syphilitic microorganisms, was initiated in 1917 by the Austrian physician Julius Wagner-Jauregg; it has been supplanted by the use of antibiotics. See also syphilis.