Cognitive impairment caused by an infection is not very common, but it is an important step in the evaluation of anyone suspected of having Alzheimer’s disease or other forms of dementia.
Many of my patients leave indelible traces in my memory, but a special place is reserved for those whose stories teach lessons that must never be forgotten. I had no idea, initially, how Marjorie’s story would join the other lessons that guide my clinical insights.* Her husband had called me, at the suggestion of a mutual friend, because of my expertise in late-life depression. Marjorie had become more withdrawn during recent weeks. She wasn’t exactly “sad,” her husband told me, and she was eating and sleeping as usual. She had stopped doing things she always loved, though, like her daily yoga practice. She seemed less engaged with her teenage children, which was very unlike her. Her memory had lost its usual sharpness recently. And, alarmingly, she was having more and more trouble working her computer and her cell phone. Her primary care doctor suspected depression and started an antidepressant, but the medication didn’t seem to be helping her.
The Human Form of “Mad Cow” Disease
As a geriatric psychiatrist, I recognized that Marjorie’s symptoms warranted careful evaluation. Even though she was only in her late 50s, very young for the onset of a dementia, her problem seemed unlike a routine case of depression. Her memory difficulty and her trouble carrying out tasks that had been simple a few months earlier suggested a neurocognitive problem such as delirium or dementia. The careful work of a local neurologist to whom I referred Marjorie led to a sad discovery. Marjorie was suffering from Creutzfeldt-Jakob disease, an infection of the brain that produces rapidly progressive dementia. Creutzfeldt-Jakob disease is a transmissible spongiform encephalopathy, sometimes called the human form of “mad cow disease,” and is caused by microscopic particles called prions, which are simple and potentially devastating proteins that cause certain host proteins to undergo a destructive change in shape. Although no curative treatment is available for this disorder, recognition of the diagnosis allowed Marjorie’s family to prepare for her death and to ease her final weeks of suffering by providing a palliative and loving environment.
Rapid Recognition of Infections is Critical
Marjorie’s sad experience is a reminder that some cases of dementia are caused by infections of the brain or body, but not all these infections are as relentless as was hers. Recognition of an infection is critically important because some infections, detected early enough, can be halted or even reversed. Discovery of a treatable infectious cause of cognitive impairment is not very common, but it is an important step in the evaluation of anyone suspected of having Alzheimer’s disease or another dementias.
Other Brain Infections
Infections that directly affect the brain are often missed by routine blood tests. Special testing is necessary to identify some of the most important brain infections that affect cognition.
HIV and AIDS
HIV infection, for example, can lead to the full range of neurocognitive symptoms from mild to severe. Cognitive impairment with HIV infection may be the first manifestation of AIDS, and this is often accompanied by problems with movement, speech, and behavior.
Syphilis is another transmissible infection that can produce severe cognitive changes in its later stages. It is possible to overlook or miss the significance of the earlier stages of infection.
Lyme disease, a common infection in northeastern and some southern regions of the United States, should be considered when evaluating a person whose cognitive ability has changed.
A Long List
These and many other central nervous infections can act directly on the brain through production of neurotoxins as well as more indirectly through initiating an inflammatory reaction that produces toxic byproducts. The list of potential brain infections is a long one that includes prions, fungi, bacteria, and larger parasitic organisms. Many infections are responsive to treatment.
Infections of the Body
In addition to the infections of the brain, another class of infections must be considered when evaluating a new cognitive change. These other diseases, located outside the central nervous system, are often treatable and sometimes cause great harm before they are discovered. Infections of the urinary tract or lungs are very common in older people who show the rapid change in alertness, attention, memory, and orientation called delirium. Delirium is often reversible once the cause is identified and treated. Simple blood tests and cultures of urine, blood, or sputum are used when clinicians search for these infections and for the antibiotics that will cure them.
Tips for Family Members
What should a patient, or a patient’s family, do to make sure that infections are not overlooked in someone with suspected Alzheimer’s disease or another dementia? First and foremost, make sure to express your concern to the clinicians who are caring for someone with an altered mental state. Also, it is crucial to ensure that the patient’s history is known by his or her health care providers. This is especially important if the cognitive changes are recent, or developed rapidly, or were associated with a known medical illness or known exposure to an infectious disease. Identifying an infection can require special tests of blood or cerebrospinal fluid that are not routinely ordered in many treatment settings. Awareness of a disease history or of an exposure may lead to further assessment and earlier identification of an infection even when typical medical symptoms such as fever, cough, or pain with urination are subtle or absent.
Some infections, like Marjorie’s, cannot be cured. Her inevitable death was caused by a disease that is kept largely under control by public health measures that prevent us all from being exposed to infected beef. The cognitive effects of other brain infections, such as Lyme disease, can be halted and controlled even when not fully reversed. Delirium-inducing infectious diseases such as urinary tract infections, among the most treatable causes of cognitive impairment, can often be cured. No infection, however, should go unrecognized, so consideration of infections is an important step in the evaluation of any person with new changes in cognitive functioning.
*Marjorie’s details have been altered to disguise her identity.
- Alzheimer’s Disease Toolkit (Helpful Information to Understand and Manage Alzheimer's Disease)
- Expert Information on Alzheimer's Disease (Articles)
- What is Dementia? (Article)
- What Causes Dementia? (Article)
- Is It Alzheimer's Disease or Dementia with Lewy Bodies? (Article)
- Medical Conditions that Can Mimic Dementia (Article)
- Normal Pressure Hydrocephalus (NPH) (Article)
- Frontotemporal Dementias (Article)
- Vascular Dementia: Reducing Risks with a Brain-Healthy Lifestyle (Article)
- "Is It Something I'm Taking?" Medications That Can Mimic Dementia (Article)
- Decreasing Your Risk of Alzheimer’s (Article)
This content was last updated on: October 2, 2018
The information provided here is a public service of the BrightFocus Foundation and should not in any way substitute for personalized advice of a qualified healthcare professional; it is not intended to constitute medical advice. Please consult your physician for personalized medical advice. BrightFocus Foundation does not endorse any medical product, therapy, or resources mentioned or listed in this article. All medications and supplements should only be taken under medical supervision. Also, although we make every effort to keep the medical information on our website updated, we cannot guarantee that the posted information reflects the most up-to-date research.
These articles do not imply an endorsement of BrightFocus by the author or their institution, nor do they imply an endorsement of the institution or author by BrightFocus.
Some of the content may be adapted from other sources, which will be clearly identified within the article.