Just because you have a tremor, does not mean you have Parkinson’s disease. Likewise not all patients with Parkinson’s have tremors further complicating matters. There are typical symptoms and signs that characterize this neurodegenerative disorder but presentation is often variable and fairly unique from one person to another.
In general the most common tremor disorders are essential tremor and Parkinson’s disease. There are some distinguishing features but early in the course of each condition they can be difficult to differentiate. Specifically an essential tremor is usually faster (5 -12 Hz), occurs during voluntary movement and does not co-exist with other abnormalities on neurological exam. The tremor in Parkinson’s on the other hand is slower (3 – 6 Hz), occurs at rest and there is usually some element of rigidity and/or slowness of movement in the affected limb or other neurological signs. In cases where diagnosis is uncertain, neuroimaging may play a role in helping to distinguish between essential tremor and parkinsonism but not Parkinson’s disease specifically.
What do I mean by parkinsonism? Parkinsonism is a broad term that refers to a group of neurological conditions that present with combinations of motor problems including resting tremor, rigidity, flexed posture, “freezing”, loss of postural reflexes and slowness of movement. Their underlying and uniting cause is an abnormality in the dopamine system of the brain with the most common form of parkinsonism being Parkinson’s disease. Parkinsonism can be further divided into those with identifiable causes and a group called Parkinson–plus disorders.
Those with recognizable causes or secondary parkinsonism may be due to a variety of factors, some reversible, others resulting in irreversible damage. They include:
- Medications (metoclopramide, certain neuroleptics which are used to treat psychotic disorders such as schizophrenia)
- Toxins (MPTP, carbon monoxide or manganese
- Infections (encephalitis)
- Tumors (of the basal ganglia)
- Vascular abnormalities such as stroke
- Normal pressure hydrocephalus
- Metabolic diseases (Hypothyroidism, Wilson disease (a genetic disorder that results in the accumulation of copper in tissues throughout the body and should be considered in people under the age of 40 who present with parkinsonism))
About 15% of people with parkinsonism are eventually diagnosed with one of the Parkinson-plus syndromes (atypical parkinsonism). This group includes:
- Multi system atrophy (MSA usually has features that include balance and gait problems, urinary issues, frequent falls, hypotension and responds poorly to levodopa treatment.)
- Progressive supranuclear palsy (PSP presents early on with falls and visual problems.)
- Corticobasal degeneration (CBD is characterized by dementia and parkinsonism.)
- Lewy body dementia (LBD presents with dementia, hallucinations and fluctuating mental status.)
Unfortunately Parkinson-plus syndromes are more serious and are less treatable than classic Parkinson’s disease. A diagnosis of atypical parkinsonism should be considered when the following clinical features are present:
- Falls early in the disease
- Symmetry of signs at disease onset
- No tremor
- Poor response to levodopa
- Dysfunction of the autonomic nervous system resulting in symptoms such as significant orthostatic hypotension (falling blood pressure when standing), erectile dysfunction and incontinence early in the disease.
- Early onset of dementia
- Rapid disease progression
As you can see, there are a variety of conditions that can mimic Parkinson’s, some with identifiable causes, others likely a result of genetic and other unknown variables. Although not complete, this list is a reflection of the complexity involved with diagnosing what may seem like a simple tremor – which is why some people are in fact left in limbo without a clear diagnosis, as their clinical presentation is not initially typical for any specific disorder. It’s a complicated process to ascertain the correct diagnosis but nevertheless accurate identification is important and relevant as it may direct management and treatment options.
Calne, Donald B., MD. "Parkinsonian Syndrome and the Definition of Parkinson's Disease." Parkinson's Disease: Diagnosis and Clinical Management. By Pramod Kr Pal, MD and Ali Samii, MD. New York: Demos, 2008. N. pag. Print.
"Parkinsonisms and Parkinson's Plus Syndromes." - Parkinson's Disease Foundation (PDF). Parkinson's Disease Foundation, n.d. Web. 28 Feb. 2014. <http://www.pdf.org/en/parkinsonism_parkinson_syndrome>.
"Parkinson's Disease: Classification-Topic Overview." WebMD. WebMD, 3 Dec. 2010. Web. 28 Feb. 2014. <http://www.webmd.com/parkinsons-disease/tc/parkinsons-disease-classification-topic-overview>.