Secondary Dementias

Secondary dementias, for the most part, begin with disease outside the nervous system.  They are not associated with a degenerative process like Alzheimer’s disease in which the pathology usually involves the brain itself and no other parts of the body.  The secondary dementias usually involve some general systemic process which affects the brain secondarily.  I have divided these secondary dementias into groups: Infection, Metabolic, Brain Tumors, and Trauma, which I hope will be have some benefit.


One important issue to remember about secondary dementias is that in many cases they are treatable dementias.  For example, thyroid dysfunction or toxic states.


Infectious Disease:

The most difficult infectious disease is called Creutzfeldt-Jakob disease (CJD).  Creutzfeldt-Jakob is a disease caused not by a virus but by an infectious protein very similar to a virus.  In the past it was quite difficult to diagnosis CJD because we didn’t have adequate neuro-imaging studies.  We used to frequently biopsy the brain in Creutzfeldt-Jokob, but in association with this biopsy there was the potential for the spread of the disease itself.  Now as one recent article suggests an MRI scan with contrast shows abnormalities of the cortical ribbon in the frontal areas.  These findings represent a typical picture associated with CJD and assist greatly in the diagnosis of this condition.

AIDS dementia complex, which is the dementia associated with HIV/AIDS used to be very common.  It’s of particular interest because the brain is one of the few if not the only organ in the body which is actually invaded by the abnormal virus like particle associated with HIV/AIDS.  AIDS dementia complex has undergone a dramatic change as it has become much less common with the new and helpful treatments for HIV/AIDS.  Twenty years ago I saw 5 patients a year with AIDS dementia complex and in 2013 I saw zero.

Cryptococcal meningitis usually occurs in individuals who have immune suppression, for example, a patient with leukemia. In the past it was difficult to diagnosis but we now have antigen antibodies that can identify it relatively easy even from the peripheral blood.  The diagnosis of Cryptococcal meningitis has changed dramatically with advances in our diagnostic tools.


Metabolic states:  One of the most common metabolic states is thyroid disease particularly hypothyroidism. I saw an executive person recently who was complaining of a difficulty with memory, unsteadiness, and weight gain. Examination showed that the individual was markedly hypothyroid and improved dramatically with treatment.  The positive treatment outcome associated with treating hypothyroidism emphases the idea that many of these secondary dementias are indeed treatable.

Deficiency states:  The most common deficiency state is a B12 deficiency.  B12 deficiency is an uncommon diagnosis but in my experience it almost always involves the peripheral nerves even prior to involving the brain.  The name for B12 deficiency used to be “combined degeneration” and this is because it involved the brain, the nerves themselves as well as a cognitive impairment.

Toxins:  The specific toxins we will discuss are heavy metals and the abuse of alcohol and drugs. More specifically the heavy metals consist of mercury and possibly arsenic. There are also, reports of people having skin toxicity from mercury causing a multi symptom disease but also involving abnormalities of the brain and cognitive function.  Abuse of alcohol and drugs and I am referring more specifically to continuous long term heavy drinking or use of drugs possibly narcotic abuse has been shown to increase the possibility of cognitive impairment.  It is known however, that a relatively small amount of alcohol and this includes two glasses of wine in men and one glass for women actually may have some preventative effect for AD.

Brain Tumors:  We have seen a few patients that have presented with weakness and confusion associated with a brain tumor.  I saw one patient who was complaining of headaches and weakness and in retrospect had some unilateral symptoms whom I thought from a clinical perspective had AD. After an appropriate examination he very clearly had a lung cancer and рак печени which had metastasized to the brain.  This can happen particularly in patients who have unilateral frontal lesions.  When the lesion is more posterior one can have weakness in the arm or leg and the diagnosis is much more obvious.  When the lesion is anterior the diagnosis may be much more difficult.


In the case of a subdural hematoma (blood clot on the surface of the brain usually caused by trauma) particular in older adults, the clinical symptom is frequently new onset headaches.  It is very important to take that particular clinical syndrome (new onset headaches) and evaluate it carefully if they have not had a history of headaches.

Normal pressure hydrocephalus (NPH) commonly referred to as “water on the brain” is associated with an increase in spinal fluid within the brain cavities.  In the past the diagnosis of NPH was difficult because we did not have adequate tools to measure long term spinal fluid pressure.  We now have developed new techniques which can actually tell us the prognosis of inserting a shunt (a tubing that reduces brain spinal fluid pressure by draining the fluid into the abdominal cavity).  This allows us to identify patients that would improve with a shunt thus improving the long term outcomes of those with NPH.


Depression is a very important issue in regards to older adults.  Depression increases as one ages and the suicide rate can be substantial in older individuals.  The important thing is that we actually have rather good treatments for depression. There are a number of anti-depressant medications which are associated with few side effects and can improve depression significantly.  Depression can produce a cognitive abnormality but the pattern is usually very different from AD and involves more pronounced attention abnormalities.  In addition, symptoms of depression can result in an increase cognitive abnormality in patients with early AD.  Often severe depression and associated depressive thoughts can contribute to the lack of attention seen in AD.


It is said that approximately 20% of individuals who present with AD have an associated depression.  This is a very important concept because patients that have a dementia or AD actually can have a substantial superimposed depression and therefore the effects can be synergistic.  The depression may exacerbate the cognitive problem itself and treatment of depression can be very gratifying.

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