Doctors tend to miss Alzheimer’s diagnosis in psychotic patients more likely than than non-psychotic ones, according to new research by Canada’s University of Toronto.
The study, “Determining the impact of psychosis on rates of false-positive and false-negative diagnosis in Alzheimer’s disease,” appeared in the journal Alzheimer’s & Dementia: Translation Research and Clinical Intervention.
Alzheimer’s is frequently misdiagnosed. Patients can often have a false-positive, meaning doctors diagnose them with Alzheimer’s even they don’t actually have the disease. On the other hand, Alzeimer’s is often missed in patients — a false-negative — because the pathology resembles other types of dementia such as frontotemporal dementia (FTD) and dementia with Lewy bodies (DLB).
Many studies have shown that the only way to correctly diagnose Alzheimer’s is by using an autopsy-based neuropathologic diagnosis rather than clinical criteria. Current estimates of the true positive rate (sensitivity) is 71 to 87 percent, while the true negative rate (specificity) is 44 to 71 percent.
Psychosis often develops due to brain pathology in neurodegenerative diseases. It can also affect diagnosis rates in Alzheimer’s patients, the actual impact is unclear. Given that a misdiagnosis of Alzheimer’s can have significant implications for clinical care, Canadian researchers set out to determine the rates of misdiagnosis in Alzheimer’s patients with and without psychotic features, using data from the Seattle-based National Alzheimer’s Coordinating Center (NACC) database.
They found that 76 percent of all patients had received a correct Alzheimer’s diagnosis, while 11.9 percent got a false-negative diagnosis and 12.1 percent a false-positive diagnosis of Alzheimer’s.
Then, researchers categorized patients by their psychosis status, using responses to questions about delusions and hallucinations on the Neuropsychiatric Inventory Questionnaire (NPI-Q), which were completed by a study informant.
Their analysis showed that psychotic patients had a higher rate of false-negative diagnosis than did non-psychotic patients as well as a lower rate of false-positive diagnosis. In short, psychotic patients with Alzheimer’s were more likely to have a missed diagnosis of Alzheimer’s but less likely to be falsely diagnosed with the disease.
Interestingly, after subcategorization, researchers determined that psychotic patients were fives times as likely to be misdiagnosed with DLB. On the other hand, patients without psychosis were more likely to be falsely diagnosed with Alzheimer’s when the actual diagnosis was vascular pathology leading to dementia.
“Our research demonstrates that in patients with neuropathologically validated diagnosis of AD, those with psychosis are much more likely to be misdiagnosed with other forms of dementia,” researchers concluded, adding that their study has “raised concern that there may be an underappreciation of how common psychotic symptoms are in AD.” They urged that in the presence of psychosis, clinicians should be less hasty to diagnose a patient with DLB.