May 21, 2015

Can Diminished Sense of Smell Become a Better Diagnostic Tool for Parkinson’s Disease?

Infographic from the Michael J. Fox Foundation for Parkinson's Research

We’ve known for years that hyposmia – reduced ability to detect smells – is typically an early warning sign of Parkinson’s disease (PD). As the graphic above shows, about 96% of all newly-diagnosed Parkinsonians have already lost some sense of smell.

I was certainly part of that 96%. In addition to an arm that didn’t swing naturally when I walked, my diminished olfactory sense was a signal my medical team really should have identified as a PD red flag long before I finally received a diagnosis.

There are a variety of non-motor symptoms of PD, including
  • hyposmia
  • chronic constipation
  • urinary urgency (including frequent nighttime urination) 
  • rapid eye movement sleep behavior disorder (in which sufferers appear to act out dreams in their sleep)
  • daytime sleepiness
  • anxiety
  • depression
Hyposmia: PD’s Best Early Indicator?
None of these conditions seems to present earlier in the development of the disease, or more regularly, than that diminished sense of smell.

The hyposmia that precedes PD could – should – be a great addition to a doctor’s diagnostic bag of tricks. In the case of PD – the earlier the diagnosis comes, the sooner treatment can begin... and the more likely that depleted dopamine can be replenished.

It’s always surprising to read that by the time most people learn they have the disease, most of their neurons that produce dopamine – the neurotransmitter that enables the brain to manage the body’s movements – have been destroyed.

Are there symptoms -- or symptom combinations – that researchers could use to accurately ID Parkinson’s while it’s still in its “prodromal” phase? That’s the disease's developmental period -- akin to the incubation period for a viral infection – during which time damage is occurring before typical symptoms begin to manifest themselves.

Why Don’t Doctors Monitor Olfactory Loss More Closely?
It’s a good question. A few possible answers:
  • Sometimes the hyposmia develops so gradually that the patient doesn’t even register and report the loss.
  • Loss of smell is also a general function of aging, just as seniors usually experience some impact on their hearing, eyesight, and sense of taste.
  • Hyposmia (and its more severe cousin anosmia, the complete loss of smell) can also be symptomatic of other conditions.
Are there very particular smells that become difficult for people with PD to recognize? As reported by the National Institutes of Health, researchers have actually identified such a list, which includes:
  • banana
  • licorice
  • pizza
  • pineapple
  • turpentine
Studies have also identified other smells that people with Parkinson's have trouble picking up:
  • dill pickle
  • wintergreen
  • mint
  • gasoline
  • smoke
  • cinnamon
  • aniseed 
  • apple 
  • lemon
  • rose
If the list gets much longer, it won't have much use.

Still... could this information help diagnosticians identify PD earlier in their patients, and thus begin treatment sooner? So far, apparently not.

But research in this area continues.

Other Reasons to Study Hyposmia and Anosmia
When people develop diminished sense of smell, their quality of life is easily jeopardized.

When people can't smell, they can no longer tell if food has gone bad. Consequences include vomiting, food poisoning, even death.

Loss of gustatory pleasure
For hundreds of millions of people, eating is one of life’s great joys. Like the pleasure in sex, there are evolutionary reasons for the pleasure in eating: it keeps us alive.

Fear of social interaction
When people know they can’t really smell, they worry about their own body odor. Those worries sometimes lead to self-imposed social isolation.

The Science
As the Michael J. Fox Foundation for Parkinson's Research reports, studies suggest that the misfolded alpha-synuclein protein that wreaks havoc on neurons first takes up position in the brain’s olfactory bulb – the part of the brain that controls smell. From there, this destroyer of dopamine-producing neurons moves to other parts of the brain, doing its terrible damage along the way. Finding the ill-formed protein and attacking it before it migrates to other brain regions could potentially halt – even prevent – the disease.

A recent study confirmed that when misfolded a-synuclein protein was injected into the olfactory bulb of mice, it moved quickly into other brain regions, disabling neurons and thus effectively shutting down dopamine production.

This science reinforces the evidence that hyposmia is indeed an early indicator of PD. The challenge now? Using the science to develop earlier diagnoses and treatments for people with PD.


Norton said...

Hi John
Some months ago you changed your neurologist and he put you on a much lower dose of Sinemet than you had been taking. Will you be updating your readers on how that is going?
Also, are you still tasking the 5htp despite your doctors reservations? If so, what dose"

John Schappi said...

Hi Norton -- Yes. I'll be doing a major update on how things are going since I've made several changes of late. But I thought I would wait for a couple of weeks since I have regular checkups schedules for early June with my geriatrician and my neurologist. Stay tuned. -- John