MIAMI BEACH – Onset time of visual hallucinations can help clinicians distinguish between dementia with Lewy bodies and Alzheimer's disease, according to a study presented at the annual meeting of the American Academy of Neurology.
Patients with dementia with Lewy bodies (DLB) or Alzheimer's disease (AD) can experience visual hallucinations, visual misperceptions, elementary auditory hallucinations, and delusions. However, little is known about how these features differ between groups in incidence or character, said Tanis J. Ferman, Ph.D.
“Is there a way to distinguish between psychoses in these two groups clinically?” asked Dr. Ferman, a psychologist at the Mayo Clinic Jacksonville (Fla.).
To answer that question, Dr. Ferman and her associates compared 108 people with DLB with 154 Alzheimer's patients. They administered the Mayo Fluctuations Questionnaire and the Neuropsychiatric Inventory to informants for each participant. A consensus diagnosis came from a clinical interview, neurologic exam, activities of daily living based on Record of Independent Living results, and a neuropsychiatric evaluation.
“For the most part, patients had mild to mild-to-moderate dementia,” Dr. Ferman said. Mean scores on the Dementia Rating Scale were 114 for the DLB group and 111 for the AD group.
About one-third of each group had ocular disease such as cataracts or macular degeneration: 35.6% in the DLB group and 31.5% in the Alzheimer's group. The groups' mean ages were similar (73 and 74 years), but the DLB group had more males (69% vs. 42%).
Patients with DLB had a higher frequency of psychotic features than patients with AD. “This was not surprising–it's part of the diagnostic criteria,” she said. A total of 63% of the DLB group experienced visual hallucinations, compared with 8% of the AD group.
The onset of visual hallucinations relative to the estimated onset of dementia was 1.7 years in the DLB group and 6 years in the AD group, making it “an absolute discriminator,” Dr. Ferman said in reply to a question from a meeting attendee. “In another study, we found that 4 years was a good cutoff for when they occur in AD vs. DLB, and that was the case in this study.”
Visual hallucination type, patient insight, and degree of distress did not differ significantly between groups. There were no differences in beliefs between groups regarding danger to self, stealing, abandonment, TV figures being real, spouses or others being someone other than who they claimed to be, or the idea that their house was not their home, she noted.
People and animals were the most common hallucination in both groups (91%). Other common hallucinations involved insects (22%) and objects (14%).
Patients with DLB, however, were more likely to see specific recurrent images (70%) than were patients with AD (45%). “One DLB patient, for example, repeatedly saw children sitting on her countertops,” Dr. Ferman said.
In addition, 32% of DLB participants were likely to experience visual hallucinations when drowsy, versus 1% of AD participants. In contrast, 57% of DLB and 90% of AD participants had visual hallucinations when fully awake. “This finding could be secondary to the excessive daytime sleepiness characteristic of DLB patients,” she said.
The researchers observed additional differences. DLB participants were more likely to have visual misperceptions, such as mistaking a lamp for a person, and elementary auditory hallucinations like hearing a car drive up.
In DLB, delusions and auditory hallucinations tended to occur only in those with visual hallucinations. With Alzheimer's patients, delusions, visual hallucinations, and auditory hallucinations occurred independent of each other, Dr. Ferman said.
“DLB patients are more likely to report the images, ignore them, or touch them, which is never reported by AD patients,” she said.