Authors: Therese Scott Duncan, Jamie Luckhaus, Sara Riggare, Uppsala University, Sweden

Reviewed by: Mónica M. Kurtis. MD, Movement Disorders Unit Director,Hospital Ruber Internacional, Madrid, Spain

Getting an accurate diagnosis of Parkinson’s disease (PD) can be a long journey. PD is a progressive neurological disorder with no single definitive lab test, so doctors rely on clinical evaluation of symptoms. Early in the disease, subtle signs may be present but not recognized as Parkinson’s, since patients with very early PD often don’t yet meet the clinical criteria for diagnosis. This means many people experience a “prodromal” phase – a period of early symptoms that occur years before the classic movement symptoms of PD become apparent.

Early clues – the prodromal phase

Research shows that Parkinson’s begins long before tremors and stiffness. Non-motor symptoms can act as early clues: for example, loss of smell, a sleep behavior disorder where people act out their dreams (called REM sleep behavior disorder, RBD), chronic constipation, and mood disorders like anxiety or depression are all recognized prodromal symptoms of PD. These issues may appear 5, 10, or even 20 years before a formal PD diagnosis. Individuals might not link these problems to Parkinson’s – after all, almost everyone has occasional sleep trouble or constipation. However, studies confirm that such symptoms, especially in combination, can foreshadow PD. Research has found that loss of smell can emerge more than 20 years prior to a Parkinson’s diagnosis. Sleep disturbances, subtle autonomic (nervous system) issues, and mood changes may also occur decades earlier. Recognizing these patterns is important because they represent the prodromal phase of Parkinson’s – a window when the disease process has begun but classic motor symptoms have not yet fully developed.

It is, however, also important to note that symptoms during the prodromal stage do not always lead to Parkinson's disease, only a small percentage of people with these symptoms go on to develop Parkinson's.

When motor symptoms appear

Eventually, Parkinson’s reveals itself through motor symptoms – the movement-related issues such as tremor, slowness of movement (bradykinesia), rigidity (muscle stiffness), and balance problems. At present, a PD diagnosis can be concluded when bradykinesia plus at least one other motor sign (like tremor or rigidity) is present. Studies indicate that motor signs only become clear after a significant loss of dopamine-producing neurons – around 40–50% of these cells may already have stopped working by the time a person meets the standard diagnostic criteria. In other words, the disease has often been progressing under the surface for years. For example, a person might notice a slight hand tremor or that their handwriting is getting smaller (a symptom called micrographia) long before they receive a diagnosis. Indeed, researchers have observed that common Parkinson’s symptoms like occasional tremor can appear up to 10 years before the disease is formally diagnosed. Often these early motor quirks are attributed to aging or other benign causes at first.

Because early signs are subtle and there is no conclusive screening test for PD, it’s common for a diagnosis to be delayed. It is not uncommon for patients to visit doctors for years with complaints of things like fatigue, stiffness, or mild tremors before Parkinson’s is finally recognized. Examples from research found that in months leading up to a Parkinson’s diagnosis, patients frequently undergo a flurry of doctor visits and tests as physicians try to pinpoint the cause of their symptoms. This reflects how challenging it can be to diagnose PD in its initial stages. Some people may even receive an incorrect diagnosis (for example, essential tremor or arthritis) before PD becomes evident.

The road to confirmation

Ultimately, a Parkinson’s diagnosis is made by a neurologist observing the classic symptoms and ruling out other conditions. The doctor will take a detailed history (including those early non-motor symptoms that might have been present) and perform a neurological exam. In some cases, additional tests like a DaTscan (a specialized dopamine transporter brain scan) are used to support the diagnosis or exclude other disorders. However, there is still no single “yes-or-no” test for Parkinson’s. It’s a clinical judgment that builds over time as symptoms evolve.

The journey to a PD diagnosis can be emotionally and physically taxing. Patients and families often feel both relief and fear when the diagnosis is finally confirmed – relief in having an explanation for the myriad symptoms, and fear of what Parkinson’s means for the future. The prodromal phase, in hindsight, helps explain those earlier health mysteries (like why someone lost their sense of smell years ago).

Identifying Parkinson’s early can be important. It can open the door to earlier treatment and interventions that might improve quality of life or potentially slow the disease. Experts are actively researching ways to detect PD sooner. For instance, ongoing studies are looking at combinations of subtle signs and biomarkers (like certain imaging, genetic, cerebrospinalfluid or blood markers) to predict who will go on to develop Parkinson’s. The hope is that one day doctors can tell someone with, say, REM sleep behavior disorder and loss of smell that they could potentially come to be diagnosed with PD, and begin neuroprotective therapies before significant neurological damage occurs.

In summary, the road to a Parkinson’s disease often begins long before the word “Parkinson’s” is ever mentioned. Prodromal symptoms lay the groundwork, followed by the emergence of motor symptoms that finally bring the patient to fulfill diagnostic criteria. Understanding this journey – and recognizing the early clues – can empower patients and doctors to reach a diagnosis sooner. In turn, an earlier diagnosis can mean earlier access to treatments, knowledge, and support to manage Parkinson’s disease as proactively as possible.