Sunday, December 04, 2011

The Reversible Causes of Dementia

I'm writing this post because the New York Times has been writing about how thyroid disorders and Vitamin B12 deficiency can be responsible for neuropsychiatric symptoms. 
Read the article about Vitamin B12 here.
Read the article about Thyroid function here.  

This is news?  When I was in medical school, the knee jerk response to memory complaints was to order labs to rule out the reversible causes of dementia: CBC, Chemistry panel, VDRL (syphilis), thyroid function tests, folate and B12 levels, urinalysis, and then perhaps a brain CT.

So let me tell you how a physician thinks about dementia.  First let me tell you what dementia is: the decline in cognitive function from a prior baseline, often seen by the patient as memory problems, beyond what would be expected with normal aging. 

A patient presents with complaints of memory problems.  The physician (usually an internist or primary care doc) takes a history: when did this start, did anything precede it, are things stable or getting worse?  What exactly is happening and is the patient actually having memory problems?  Sometimes people think they are having memory problems, but really what is happening is that they are anxious or distracted, so the information never makes it into their brain to be retrieved or remembered later.  "I told my husband to take out the trash during the Super Bowl and he didn't remember to do it."  A quick measurement of memory may be done, such as the Mini-Mental Status Exam, which tests a variety of components of cognition such as orientation, the ability to immediately recall, memory, concentration, the ability to follow directions, and the ability to copy a diagram, write a sentence, and follow a written command.  It's a simple test, and most people get perfect scores, and it's a quick way to follow progress over time.   A physical exam is done, including a neuro exam, and if there are focal findings --like the absence of reflexes or weakness, or loss of sensation, or a history of loss of consciousness, seizures, or a head injury-- these are noted. 

The only way to be 100% certain of the type of dementia is to biopsy the brain.  We don't generally do that.  Instead, we rule out the "reversible" causes of cognitive decline-- infections, thyroid disorders, neurosyphilis, folate orVitamin B12 deficiency, or metabolic problems such as confusion with markedly elevated blood glucose or neuropsychiatric symptoms with hyperparathyroidism.  Some of these illnesses are discovered with blood tests, others require a scan to look for anatomical lesions, like hydrocephalus, stroke, subdural hematoma.  If a reversible cause of dementia is found, it can be treated and it will often get better. Oh, and I should add that Major Depression can mimic mild dementia, and this too can be treated, it's called pseudo-dementia and when the depression gets better, the dementia gets better.

If a patient has dementia, and the reversible causes are ruled out, then the diagnosis of depression is based on the features of the disorder and the course it takes.  Alzheimers' disease is the most common type of dementia, and it has a progressive course with some predictability.  Patients with Alzheimer's disease will have a good recall for past events, but they may forget more recent events.  Personality and social appropriateness are preserved until well into the illness, and the early stages are often rather subtle.  Decline can take place over a few years or many years, but the course is always progressive. Medicines, such as Namenda or Aricept may be prescribed in the hopes of slowing the course, and patients with vascular dementia may be told to take aspirin to prevent future episodes.  While patients have good days and bad days, these illnesses do not remit.

Vascular dementias progress in a more step-wise course.  Patients will have a sudden onset of impairment, but things stay at that level for a while, until another event happens and there is another sudden decline. The course is less predictable with regard to what faculties are compromised when.  Some patients have both forms of dementia, or a mixed etiology. 

Other forms of dementia include Pick's disease (fronto-temporal dementia), Lewy Body dementia, and dementias associated with Huntington's Disease, Parkinson's Disease, and HIV, and dementia due to repeated brain trauma.

Okay, this is my quicky discussion of  dementia.  Please don't use this as a comprehensive resource, it's mostly off the top of my head.  Roy can pipe in with all the things I missed, I'm sure there are plenty.