She's Not Crazy Just Seeing Things
BY WILLIAM TOWNSEND, OD
Mrs. G presented to our office with a history of severe geographic macular degeneration. This 83-year-old established patient was otherwise alert, well-oriented and in remarkably good health.
When I began to question her about the primary reason for her visit, she calmly said, "My kids think I'm crazy, and they want to have me committed." She went on to describe seeing "people who aren't there, trees and branches that don't exist and patterns on the walls." Visual acuities were 10/300 OU and confrontation fields were full, but FDT showed a central scotoma. All other neurological tests were normal. Dilated fundus examination showed 2.5 disc diameter areas of RPE dropout consistent with geographic AMD. The optic nerves and other fundus features were unremarkable.
We diagnosed Mrs. G with Charles Bonnet Syndrome (CBS), first described in 1760 by Swiss philosopher Charles Bonnet, whose visually impaired grandfather described seeing animals and buildings that Bonnet couldn't see. An estimated 13 percent of patients who have AMD experience some degree of CBS. Sensory deprivation (living alone), diminished cognitive abilities, stroke, aging and depression can exacerbate the disease. CBS occurs when people who have vision loss see objects that they intellectually know aren't real. The onset usually occurs soon after an episode of vision loss or worsening of existing visual impairment.
Two primary patterns of visual hallucination may affect individuals who have CBS. First is the occurrence of repetitive patterns such as mosaics or tree branches. Second is the appearance of people or faces, either normal in size or reduced. Our patients have reported seeing animals or even dragons as part of CBS.
The precise etiology of CBS is unknown, but clinicians theorize that it occurs in response to sensory stimulation. A similar situation exists in individuals who have lost limbs. They complain of pain, cold or tingling in limbs that have been amputated.
It's important to differentiate between CBS and other conditions that present with visual hallucinations. Between eight percent and 40 percent of patients undergoing long-term treatment for Parkinson's disease will have visual hallucinations. They're also the most common type of hallucination in dementia, a syndrome characterized by multiple cognitive deficits and severe memory loss.
Alpha-adrenergic anti-hypertensives such as clonidine, the anti-convulsant carbamazepine, analgesics such as pentazocine and fentanyl, and anti-vertigo drugs such as diphenidol may cause hallucinations. Selective serotonin re-uptake blocker antidepressants (SSRI) and some histamine-2 blockers used to treat gastric disease may also generate hallucinations.
Space-occupying lesions in the brain, particularly occipital lobe tumors, may cause hallucinations. When patients present with visual hallucinations not associated with seizures, make every effort to rule out an occipital lobe lesion.
Making the Diagnosis
When patients present with complaints of visual hallucinations, it's vital to establish whether the cause is organic or benign. If patients recognize that their experience isn't real, but rather imagined, this suggests CBS. Careful evaluation of the individual's mental status, ability to verbalize, comprehend and think rationally can help you determine if the likely cause of visual hallucinations is CBS or another, more threatening condition.
Dr. Townsend is in private practice in Canyon, Texas, and is a consultant at the Amarillo VA Medical Center. E-mail him at firstname.lastname@example.org.