It’s Not Always Alzheimer’s Disease

Consider the following case: a 78-year-old man with a diagnosis of Alzheimer’s disease comes to your clinic for evaluation of “bad behavior.” He was already started on donepezil and memantine several years ago by a neurologist due to memory complaints and erratic behaviors. He is irritable and inappropriate in the office, and his family wants you to address his behavioral problems. What do you do? 

Too often, the management of these cases assumes that the baseline diagnosis is correct and proceeds accordingly. But is every case of presumptive cognitive impairment actually Alzheimer’s disease? With nearly 50% of elderly individuals 85 years and above having Alzheimer’s, this would seem to be a reasonable assumption.  However, this assumption is not always true, and misdiagnosis can compromise treatment.

In addition to a baseline medical and psychiatric evaluation, it is important to make certain that the following four items have been completed:

• Longitudinal history of cognitive, functional, and behavioral changes
• Medical evaluation
• Brain imaging
• Neuropsychological testing

The longitudinal history will indicate whether there is progressive decline, which defines the diagnosis. A medical evaluation (including medication review and laboratory studies) will rule out any obvious alternative causes, such as hypothyroidism or Vitamin B12 deficiency.

Structural brain imaging such as a CT or MRI will help to assess the relative roles of strokes, tumors, bleeds, or other brain pathology; a PET scan using fluorodeoxyglucose or FDG scan can identify the presence of cerebral hypometabolism, while newer amyloid-based PET scans can identify the presence of amyloid protein.

Finally, neuropsychological testing can establish the pattern and degree of cognitive impairment. Put together, this information will provide the most accurate diagnosis of a potential neurocognitive disorder such as Alzheimer’s disease—or an alternative diagnosis.

In the case presented, the longitudinal history did not indicate any decline over the past two years, which is not consistent with Alzheimer’s disease. Baseline medical evaluation and brain imaging were unrevealing. Neuropsychological testing, however, showed relatively intact short-term memory, a finding that is definitely not consistent with Alzheimer’s disease or any other form of neurocognitive disorder. The “bad behaviors” were more consistent with longstanding impulsivity. In this case, cognitive enhancing medications were not necessary. A low-dose antipsychotic did, however, lead to vast improvement in demeanor, concentration, and behavior.

What are some of the great mimics of Alzheimer’s disease in older patients? Consider the presence of alcohol abuse, bipolar disorder, attention deficit disorder, and medication-induced impairment, to name just a few.

How often do you reconfirm a diagnosis of Alzheimer’s disease?

Marc E. Agronin, MD is Medical Director for Mental Health and Clinical Research,Miami Jewish Health Systems, Miami,   FL. He also is Affiliate Associate Professor of Psychiatry and Neurology, University of Miami Miller School of Medicine, Miami, FL.

The views expressed on this blog are solely those of the blog post author and do not necessarily reflect the views of Psych Congress Network or other Psych Congress Network authors.