Learn about medical disorders that can interfere with cognition and mimic dementia.
Even as a sleep-deprived and inexperienced intern, several decades ago, I knew something was wrong when I was asked to evaluate Mrs. M, a woman well into her 90s who was admitted for care of “dementia.” She was reputed to have been sharp as a tack until the preceding week. Following the operation that repaired her cataracts, which in those days meant a period of patched eyes and bedrest, her behavior changed quickly and dramatically. Her lovely personality became irritable and angry. Her language became abusive. She scratched a caregiver in her nursing home who was trying to help her get dressed.
It seemed very likely to me that Mrs. M’s sudden change in behavior had more to do with her operation than with a progressive neurological condition.
A Condition that Can Fool Even Experienced Doctors
In fact, Mrs. M was suffering from delirium, at that time called Acute Organic Brain Syndrome that results in rapidly changing mental states, and causes confusion and changes in behavior. She returned to her previous healthy cognitive status very quickly after her eye patches were removed and her post-operative recovery continued.
The lesson I learned from her recovery was that delirium can fool even experienced doctors into misdiagnosing dementia, which is now called Major Neurocognitive Disorder (and which I’ll abbreviate after this as MaND). Delirium shares with MaND the features of confusion, disorientation, and memory impairment.
Delirium looks very different, though, in other ways. It comes on rapidly, often after a medical or surgical event or toxic combination of medications. It is accompanied by shifting alertness, resulting in moments of sleepiness alternating with moments of agitation. Delirium is more often associated with visual hallucinations or psychotic delusions than MaND. And, most importantly, delirium can often be reversed once the cause is found and treated.
Its causes are many and include infection, metabolic disturbances, toxic medication reactions, withdrawal from alcohol, and the effects of head injury, just to name a few.
Delirium is only one of a long list of reversible or partly reversible medical conditions that can mimic MaND and mislead the doctors into assigning the wrong diagnosis. When the patient’s condition is labeled incorrectly, some terrible things begin to happen. The search for treatable conditions may be stopped too early. Hopelessness can set in. The wrong medication might be prescribed. The opportunity to improve the patient’s health and quality of life may be lost, perhaps forever.
What makes this especially tragic is that distinguishing delirium from MaND is usually not too difficult and just requires careful attention to history, symptoms, physical and mental status examinations, and the results of common laboratory tests.
I’m going to discuss a few of the many medical disorders that can interfere with cognition and mimic MaND. I’ll leave discussion of the medications that interfere with cognition for another article. The systems and organs of the body are so dependent upon each other that it will not surprise you to learn that many different kinds of disorders can present with real or apparent memory disturbances.
Starting at the top of the body, head injury tops the list because of the risk of trauma to the brain. A fall, even one that seemed less serious, can be followed by significant cognitive problems. When this is due to a concussion, symptoms usually improve over time with supportive care. A limited post-traumatic bleed inside the skull can interfere with cognitive functioning by leading to a collection of blood called a subdural hematoma.
Normal Pressure Hydrocephalus
Another condition that can create cognitive impairment is normal pressure hydrocephalus (NPH), a disorder in which cerebrospinal fluid accumulates in the ventricles (cavities) of the brain and interferes with thinking, memory, walking, and control of urination.
Problems with Vision and Hearing
Sensory limitations, too, can create a picture like cognitive impairment that worsens as the affected person becomes increasingly isolated as a result of hearing or vision problems. Recent research has emphasized that there is a relationship between hearing loss and the risk for development of cognitive impairment.
Disorders of the Heart and Lungs
The heart and lungs provide the brain with oxygen and nutrients that are necessary for proper functioning. Age is often accompanied by vascular (blood vessel) disease that interferes with cardiac output or lung disease that interferes with the delivery of oxygen to the brain. These underlying diseases can cause MaND as well as what’s commonly known as vascular dementia (which can sometimes occur along with Alzheimer’s-related dementia). They can also affect alertness, memory, and executive function..
Liver and Kidney Disease
Diseases of the kidney or liver can result in an accumulation of toxic metabolic waste products in the blood, dulling the mind or poisoning mental activity and sometimes resulting in MaND.
Disorders of the endocrine organs, responsible for making hormones that are transported through the bloodstream in order to control many metabolic activities, are additional causes of MaND-like symptoms. An excess or deficiency of thyroid hormone interferes with thinking. Disturbances in the regulatory effects of insulin, a hallmark of diabetes mellitus, harm cognition along with other bodily functions.
Some infections produce a prolonged change in mental functioning that lacks signs clearly linked with delirium. Lyme disease, syphilis, or HIV for example, are capable of mimicking MaND.
Heavy metal toxicity, too, can create more stable changes that could go unrecognized without specific testing.
Cancers of various types can affect cognition through brain tissue destruction, increased pressure within the head, or sometimes even through producing chemicals that travel from various parts of the body through the blood stream to the brain where they create havoc.
How Doctors Make an Accurate Diagnosis
Fortunately, many of these medical conditions are treatable and some are even curable. An assessment for MaND should always include tests to look for these treatable conditions so that no patient has to suffer needlessly from an untreated and debilitating condition. The mental status examination should give clues to the presence of a delirium or certain other medical disturbances, and this examination is followed up by physical examination and tests of the blood and urine.
Blood count, thyroid tests, kidney functions, liver enzymes, metabolic screening, and urinalysis are routine elements of the MaND diagnostic workup. Lyme or syphilis tests, lumbar puncture, heavy metal screen, urine culture, chest X-ray, EEG, or neuroimaging with MRI and/or PET scanning may be appropriate tests for patients whose symptoms suggest the need for these additional, more costly, and sometimes more invasive tests.
Mrs. M’s recovery from delirium showed her caregivers that sometimes even a severe cognitive disturbance can be effectively treated. It is the clinician’s job to think beyond the diagnosis of MaND and consider other possible causes of symptoms, some of which may be treatable. Recognizing the medical mimics of MaND opens the door to treatment, recovery, and better quality of life for patients and those who care for them.
- Alzheimer’s Disease Toolkit (Helpful Information to Understand and Manage Alzheimer's Disease)
Infections that Can Cause Dementia (Article)
This content was last updated on: October 10, 2017
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