To the Editor: Charles Bonnet syndrome refers to formal, complex, persistent, stereotypical visual hallucinations that are not accompanied by any other psychotic symptoms in cognitively unimpaired individuals (1). Although multiple sclerosis can produce diverse neuropsychiatric manifestations, we know of no reports of Charles Bonnet syndrome in patients with this illness.

A literature search revealed that a greater risk of Charles Bonnet syndrome has been found with advanced age, cerebral impairment, and ocular pathology (2). It is therefore not unusual that Charles Bonnet syndrome has been found in younger people with certain diseases involving the eyes and brain. Therapy targeting the underlying ocular or cerebral diseases might alleviate the hallucinations. In addition, anticonvulsants such as carbamazepine and valproate are effective for treatment because their antiseizure properties can reduce "irritable cortex," a condition that has been hypothesized to cause a "phantom visual phenomenon" (3). Despite prevalent ocular and cerebral involvement in multiple sclerosis, to our knowledge, there have been no reports of hallucinations that are consistent with the Charles Bonnet syndrome. Plausible explanations are 1) that visual hallucinations seldom occur without cognitive impairment and other psychotic symptoms in multiple sclerosis, 2) that there are few voluntary expressions of visual hallucinations, and 3) that physicians are unfamiliar with this syndrome. The last two explanations might account for an underestimation of Charles Bonnet syndrome in multiple sclerosis. It is suggested that psychiatrists, neurologists, and ophthalmologists pay more attention to the nature of hallucinations in order to diagnose Charles Bonnet syndrome, which can be treated effectively with anticonvulsants.