I am frequently asked why I use the term “parkinsonism,” rather than “Parkinson disease” (PD) for most patients. It is a fair question, and one that I hope to clear up here. This issue is also relevant for veterans seeking service connection for PD through the U.S. Department of Veteran Affairs (VA). If notes from a doctor’s office indicate parkinsonism as the diagnosis, the vet may be denied because the VA interprets the use of “parkinsonism” as an indication the patient “does not have a diagnosis of Parkinson disease,” or so the denial letters read. In my practice I have written a form letter to explain the situation to the VA.
Parkinsonism is an umbrella term most movement disorder neurologists use to refer to a group of conditions that share features (physical signs) of PD. People who have parkinsonism may have PD, or may have an alternative diagnosis which can mimic PD, such as vascular parkinsonism, drug-induced parkinsonism, or multiple systems atrophy – to name a few. When we say that someone has parkinsonism, we are talking about these signs: slowness of movement (bradykinesia) plus either stiffness of muscles (rigidity) or tremor at rest. Balance problems and gait changes are often considered as well. All of these are so-called “parkinsonian features.” There are a variety of other early motor and non-motor signs and symptoms which may support a diagnosis, but are not required to say that one has parkinsonism.
Parkinsonism is a less specific descriptor than PD, and is not an actual diagnosis, but a category reflecting a set of symptoms. The term is sometimes used out of necessity, even when it seems pretty likely that a person has PD. But there is a world of difference between pretty likely and definite.
Under diagnostic criteria by the American Academy of Neurology (AAN) the best we can say in the vast majority of cases is that a person has “probable” PD (1). However,when doctors diagnose patients they have to choose an ICD-10 (Medicare billing) code. There is no code for probable PD, but there are codes for parkinsonism and PD. Under the guidelines the only coding choice that makes sense most of the time is parkinsonism.
It is also true that in rare cases, some mimickers look identical to PD, especially early in disease. It may take a while, sometimes years, for atypical forms of parkinsonism to “declare” themselves and show signs or symptoms that agree with something other than PD.
Because of this overlap in presentation, under National Institute of Neurological Disorders and Stroke (NINDS) criteria (2), brain biopsy would be the only way we could be certain, and diagnose definite PD in a living person. However, NINDS does not condone brain biopsy, no one does (see below). NINDS therefore tells doctors the highest degree of certainty they can have is “probable PD.” The internationally recognized Movement Disorder Society (MDS) guidelines also recognize “probable PD” as a diagnostic endpoint for the same reason. There are a variety of guidelines around the world which are very similar: PD is a clinical diagnosis and brain biopsy, while it would diagnose with certainty, would be unethical (4). You are using your brain, all of it, and would probably miss pieces that were removed. Likewise, this would place you at risk of infection, bleeding, or other issues.
Sometimes people donate their brains to science (after they have finished using them). At that point, it can be established conclusively whether or not a person had suffered from PD in their lifetime. This is often helpful for other family members and does a lot to move neuroscience forward. Several of my patients have in recent years used the Mayo Jacksonville lab for this reason. When donated brains are examined, pathologists are looking for Lewy bodies (LB), the pathologic hallmark of disease (see footnote) in key locations of the brain. Location is important, because PD is not the only condition with LB. Other diseases that have LB in a pattern different from PD include pure autonomic failure (PAF), multiple systems atrophy (MSA), and Lewy body dementia (LBD).
Back to the living. Diagnosis can sometimes be supported by dopamine transporter scanning (DaTscan) but this is still not definitive. DaTscan tells doctors that dopamine is low, but not the reason why. The FDA indication for DaTscan is to distinguish essential tremor from parkinsonian syndromes. That is usually not a hard call.
So, to sum up the problem, we can’t biopsy your brain, and there is no blood test, imaging, cerebrospinal fluid examination, or other electrophysiology test that makes the diagnosis of PD. Until we have a test or a biomarker, PD will remain a clinical diagnosis, and patients will have “probable” PD or parkinsonism.
Footnote: For more on Lewy bodies, read the spring 2016 MPDN article “What’s so bad about alpha-synuclein.”
REFERENCES
- Suchowersky, et al. Practice Parameter: Diagnosis and prognosis of new onset Parkinson disease (an evidence-based review) Report of the Quality Standards Subcommittee of the American Academy of Neurology. Neurology. 2006 Apr 11;66(7):968-75.
- Gelb, et al. Diagnostic criteria for Parkinson’s disease. Arch Neurol. 1999;56:33-39.
- Postum and Berg, MDS Clinical Diagnostic Criteria for Parkinson’s Disease (I1.010) 2016; 86 (16 Supplement).
- Marsili, et al., Diagnostic Criteria for Parkinson’s Disease: From James Parkinson to the Concept of Prodromal Disease. Front Neurol. 2018; 9: 156.
