Parkinson’s Disease: Early Warning Signs

By: Kristi Riker, OTD, OTR/L

Parkinson’s Disease: Early Warning Signs

How long did it take to receive your Parkinson’s disease (PD) diagnosis? Many individuals see multiple doctors and experience confusing symptoms for years before receiving a clear diagnosis. This is partly because there is currently no single definitive test for PD. Instead, doctors rely on a combination of methods.

Common Diagnostic Approaches

• Neurological exam: Evaluates movement symptoms such as resting tremor, slowness, muscle rigidity, and changes in balance or gait

• Medication response: Improvement with levodopa can support a PD diagnosis

• Brain imaging: MRI, CT scans, or DaTscans assess dopamine-producing neurons

• Smell testing: Evaluates the olfactory system, which is often affected early

• Skin testing: Emerging research examining chemical compounds in skin oil

• Blood tests: Investigating biomarkers linked to PD (still developing)

• Canine detection: Research shows trained dogs may be able to detect PD from skin samples (Rooney, 2025)

Why Diagnosis Can Take Time

Early symptoms of PD are often subtle and can mimic other conditions. Research suggests symptoms may begin up to 20 years before a clear diagnosis. Parkinson’s can start long before noticeable tremors or movement issues—this is known as the prodromal stage.

Key Early Warning Signs:

• Loss of smell (hyposmia): One of the earliest and most studied markers. About 80% of people with PD experience reduced smell, which may appear up to 20 years before diagnosis (Lo, 2021).

• REM sleep behavior disorder: Acting out dreams (kicking, punching, or moving during sleep) can appear years—even decades—before motor symptoms.

• Chronic constipation: Linked to early changes in the gut nervous system.

• Mood changes: New-onset depression or anxiety later in life may precede diagnosis.

• Autonomic changes: Issues with body systems not under conscious control, such as low blood pressure when standing, urinary problems, or erectile dysfunction.

• Voice changes: A softer voice, slurred speech, or monotone tone may be early signs.

• Facial expression changes: Reduced facial expression, sometimes called “masked face.”

• Subtle motor changes: Smaller handwriting, slight slowness, stiffness, or muscle cramps before noticeable tremor.

The “Gut-First” Parkinson’s Theory

One of the most exciting areas of research suggests Parkinson’s may begin in the gut rather than the brain. Researchers have found that abnormal clumps of the protein alpha-synuclein—a hallmark of PD—can appear in the digestive system years before brain symptoms.

Scientists believe these proteins may travel from the gut to the brain via the vagus nerve, which connects the intestines and brain. This may also explain why many individuals experience long-term constipation years before diagnosis.

If this theory holds true, future treatments may focus on:

• The gut microbiome

• Inflammation in the digestive system

• Preventing the spread of alpha-synuclein early

  
  

As one study explains, gut-based interventions could allow treatment during early stages—before motor symptoms develop (Oliver, 2025).

What Could Future “Gut-First” Treatments Look Like?

Improving gut health

• Personalized probiotics or prebiotics

• Diet plans to support healthy gut bacteria

• Fecal microbiota transplant (FMT)

Reducing gut inflammation

• Anti-inflammatory medications

• Nutrition strategies targeting inflammation

• Strengthening the intestinal barrier

Targeting alpha-synuclein

• Vaccines or antibodies

• Medications to prevent protein clumping

• Therapies to help clear abnormal proteins

  
  

Interrupting gut–brain signaling

• Blocking spread through the vagus nerve

• Medications that stop protein transmission

• Neuromodulation techniques

Why Early Warning Signs Matter

Recognizing early signs of Parkinson’s is critical. If identified before significant brain cell damage occurs, treatments may be more effective in slowing progression.

Early awareness allows individuals to:

• Begin treatment sooner

• Adopt healthy lifestyle habits (exercise, nutrition)

• Improve quality of life

• Prepare for emerging therapies

While we cannot yet reverse the disease, early detection creates a powerful window of opportunity to slow progression and improve long-term outcomes.

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References

Lo C, Arora S, Ben-Shlomo Y, Barber TR, Lawton M, Klein JC, Kanavou S, Janzen A, Sittig E, Oertel WH, Grosset DG, Hu MT. Olfactory Testing in Parkinson Disease and REM Behavior Disorder: A Machine Learning Approach. Neurology. 2021 Apr 13;96(15):e2016-e2027. doi: 10.1212/WNL.0000000000011743. Epub 2021 Feb 24. PMID: 33627500; PMCID: PMC8166425.

Oliver PJ, Civitelli L, Hu MT. The gut-brain axis in early Parkinson's disease: from prodrome to prevention. J Neurol. 2025 May 21;272(6):413. doi: 10.1007/s00415-025-13138-5. PMID: 40394204; PMCID: PMC12092510.

Sui X, Zhou C, Li J, Chen L, Yang X, Li F. Hyposmia as a Predictive Marker of Parkinson's Disease: A Systematic Review and Meta-Analysis. Biomed Res Int. 2019 May 19;2019:3753786. doi: 10.1155/2019/3753786. PMID: 31236405; PMCID: PMC6545790.

Rooney N, Trivedi DK, Sinclair E, Walton-Doyle C, Silverdale M, Barran P, Kunath T, Morant S, Somerville M, Smith J, Jones-Diette J, Corish J, Milne J, Guest C. Trained dogs can detect the odor of Parkinson's disease. J Parkinsons Dis. 2025 Sep;15(6):1111-1115. doi: 10.1177/1877718X251342485. Epub 2025 Jul 14. PMID: 40659046.