These diseases, which include multiple sclerosis and diffuse sclerosis, are due to the degeneration of the insulating (myelin) sheath around nerve fibers, and its replacement by scar tissue. The cause of this degeneration is unknown.Although these disorders are structural and neurological, they are included in the American Psychiatric Association’s Diagnostic and Statistical Manual (1952) under “Chronic Brain Syndromes associated with diseases of unknown or uncertain cause,” since they are frequently accompanied by personality disturbance. The psychiatric symptoms may, in fact, be so pronounced as to mask the organic picture and make correct diagnosis difficult.In multiple sclerosis there is no characteristic psychiatric syndrome; the symptoms depend largely on the basic personality of the individual patient. Frequently there is an accentuation of pre-illness trends. One of the more common symptoms is an exaggerated cheerfulness or even euphoria, which is doubtless a compensatory reaction to the destructive effects of the disease. Another common symptom is marked irritability, and a third is emotional instability. In cases where nerve destruction has progressed to a marked degree, emotional control may become so impaired that the patient may have a sudden compulsion to laugh or cry, without experiencing the feelings that usually go with these reactions. There may also be some intellectual impairment. In addition, paranoid, hypomanic, and depressive reactions are occasionally found in multiple sclerotic patients.In diffuse sclerosis, particularly Schilder’s disease, extensive demyelini- zation occurs in the cerebral hemispheres. Since different areas may be affected in different cases, the major features of the disease vary widely. Neurological symptoms may include cortical blindness, hemianopsia (half vision in each eye), optic atrophy, and all varieties of motor and sensory disturbances. These symptoms are frequently accompanied by headache, vomiting, vertigo, and convulsions. Sometimes the clinical picture is similar to that in brain tumor; and early in the course of the disease diffuse sclerosis may be confused with hysterical and schizophrenic reactions. Common psychological symptoms are memory defect, apathy or irritability, personality changes, and, in some cases, confusion, disorientation, and general mental deterioration.Diffuse sclerosis runs a rapid course, although remissions occasionally occur. The terminal stages are characterized by dementia and paralysis of all the limbs. No effective treatment has been found for this disorder.