Why Early Symptoms Matter
By the time classic motor symptoms appear, a large proportion of dopamine-producing neurons in the brain have already been lost. Researchers and clinicians have therefore been exploring prodromal (pre-diagnosis) features that could help identify people at higher risk of Parkinson's many years earlier.
Important: Having one or more of these symptoms does not mean a person will develop Parkinson's disease, but when present together, especially with other risk factors like a family history, they can warrant further clinical evaluation.
Four Early Symptoms Potentially Linked with Parkinson's Disease
1. Loss of Sense of Smell (Anosmia)
A gradual decline in the ability to detect odours is one of the most common early features observed in people later diagnosed with Parkinson's disease. This loss may begin years or even decades before motor symptoms. Over 90% of individuals with Parkinson's experience this change in smell sensitivity.
Smell loss can also occur for other reasons (e.g., sinus infections, respiratory conditions), so its presence alone doesn't confirm Parkinson's. However, noticeable, sustained smell loss, especially in middle age or later may prompt further investigation.
2. REM Sleep Behaviour Disorder (RBD)
In healthy REM sleep, most of the body's muscles are temporarily paralysed so we don't physically act out dreams. In REM sleep behaviour disorder, this paralysis is absent, leading to dream enactment such as talking, reaching, or kicking during sleep.
Studies show that people with RBD, particularly those over age 50 have a substantially higher likelihood of developing Parkinson's or related neurodegenerative conditions over the following years.
3. Chronic Constipation
While common in the general population, persistent constipation (lasting weeks or longer) is seen more often in people who later receive a Parkinson's diagnosis. Two-thirds of individuals with Parkinson's report chronic constipation, suggesting involvement of the enteric nervous system (nerves lining the gut) early in the disease process.
This symptom may reflect broader neurodegenerative changes and is an area of ongoing research into links between the gut and the brain in Parkinson's disease.
4. Dizziness or Lightheadedness When Standing (Orthostatic Hypotension)
A significant drop in blood pressure upon standing leading to dizziness or lightheadedness can also be seen in people years before a Parkinson's diagnosis. Although evidence for this symptom as a prodromal marker is not as strong as for smell loss or RBD, chronic orthostatic hypotension may indicate autonomic (nervous system) involvement.