Since my thorough neuropsychological evaluation for cognitive impairment in late August, I've been nervously awaiting the results, which had been delayed in part by the government shutdown, including the National Institutes of Health (NIH).

Last Tuesday, I finally got them: the tests were completely normal; there's no sign of cognitive impairment.

This is, of course, wonderful news and should be a great relief.

I tend, however, to be a glass-half-empty kind of guy, and I don' feel much relieved: I've traded a diagnosis (Alzheimer's disease) for a set of disturbing symptoms with no reasonable explanation.

In case you've been reading these posts only occasionally, let me summarize my situation.

About three years ago I started having symptoms of cognitive impairment (getting lost, inability to perform certain bookkeeping responsibilities, increasingly poor memory, losing things constantly, and so on).

Two years ago I visited a neurologist who administered the usual cognitive testing, which revealed mild impairment. Repeat testing a year later also show a mild degree of impairment. Other major causes of cognitive impairment were ruled out, so I was left with a diagnosis of Mild Cognitive Impairment (MCI), probably Alzheimer's. This blog has been a description of my ongoing experience with this impairment.

As part of research studies that I've participated in, I have had three brain scans over the past eight months, none of which has shown any sign of Alzheimer's disease.

This most recent neuropsychological set of tests at NIH was very intensive and extensive, about four hours in length. Unlike the previous, less thorough tests of cognitive function, this more rigorous evaluation shows no sign of cognitive impairment.

So I now have a set of symptoms that have impaired me for several years but for which I can find no reasonable explanation.

The reason I have avoided making entries in this blog over the past week is that I haven't known what to write; this has so stunned me that I've had to talk it through with family and some friends.

So far, I can't explain it in any reasonable way. Here are some of the thoughts I've had:

Perhaps my previously diagnosed cognitive impairment has resolved and I've gotten better.

Unlikely. My symptoms haven't gone away. Also, any cause of cognitive impairment (of longer than six months) that might improve with time (vitamin B-12 deficiency, for instance) has been medically ruled out. These things just don't get better.

Perhaps all the brain scans and the neuropsychological tests have been wrong.

Unlikely. Any medical test, of course, can be normal even when the disease is present. In the case of the tests I've taken, this "false negative" rate is very roughly 10 percent for each. Mathematically, that means that there is more than a 99.99 percent chance that at least one of the tests would be positive if I had Alzheimer's.

Perhaps it's some other form of cognitive impairment.

Unlikely. Not only have I been thoroughly evaluated to rule out the other reasonable causes, but the intense cognitive testing indicates no sign of impairment for any reason.

Perhaps I'm imagining it.

Always a possibility, but people very close to me have also seen obvious evidence of impairment for several years and no one, including a trained psychologist who knows me well, finds this possibility credible. I don't either.

There are a number of other possibilities I'll explore in later posts, but for now, any explanation I've been able to come up with is highly improbable.

As I written before, all of this can be extremely unsettling. For several days last week, I felt quite unmoored.

I'd come to terms with my identity as an Alzheimer's patient and now it has become, at the very least, uncertain. This life over the past year as an Alzheimer's patient has become very meaningful and fulfilling.

What am I now? What am I going to do?

But after lots of conversation with friends and family, I no longer feel so unmoored. This is but one more twist in a bumpy, uncertain road. I can trust myself and my perceptions. I can simply wait for the next step in this strange journey. I feel ready to let go and see what exciting things will happen.

These test results, whatever they ultimately mean, are good news.

At the very least, the impairment I perceive is progressing very slowly. At the very least, this is another opportunity to learn to live with uncertainty, just as most people with mild cognitive symptoms have to. It's an opportunity to let go of self.

This wild ride continues.

Editor's note: David's journey with Mild Cognitive Impairment was chronicled in "Fade to Blank: Life Inside Alzheimer's" an in-depth look at the real lives of families impacted by the Alzheimer's epidemic. His story continues on his personal blog on AgingCare.com.