Parkinson’s Disease

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Parkinson’s disease (PD) is a progressive neurodegenerative disease that causes neurons in the area of the brain that controls movement, to weaken and die. Healthy neurons produce dopamine, which the brain needs in order to regulate movement, weakened neurons produce lower levels. The cause of this weakness is currently unknown. 

Some patients with PD also suffer from a decline in norepinephrine, which is known to transmit signals across nerve endings and controls various physiological functions, such as blood pressure and heart rate.

Tremor occurs in more than 75% of PD patients and is known to significantly reduce quality of life. Tremor causes functional interference in more than 60% of PD patients during daily activities such as dressing, fine motor skills, and writing.

First depicted by James Parkinson in the well-known 1817 monograph, “An Essay on the Shaking Palsy”, PD is an ever-evolving neurodegenerative illness that effects somewhere in the range of 100 and 200 for every 100,000 individuals over 40 years old, and more than 1 million individuals in North America alone.

PD is uncommon in people younger than 40, and the incidence of the disease increases rapidly for people over 60 years.  The mean age at diagnosis is 70.5 years.

In most populations, genetics explains 3–5% of PD.  This is linked to known 90 PD genetic risk variants which collectively explain 16–36% of the heritable risk of non-monogenic PD.

Causal associations that can double the risk of PD include:

Having a relative with Parkinson’s disease or tremor
Being a non-smoker
Constipation

The diagnosis is clinically based, where supplementary testing is reserved for people with an atypical presentation.

Current criteria define Parkinson’s disease as the presence of bradykinesia combined with either rest tremor, rigidity, or both.

However, the clinical presentation is multifaceted and includes many non-motor symptoms, such as postural instability.

While PD has traditionally been considered a motor system disease, it is now recognized to be a complex condition with diverse clinical features that include neuropsychiatric and other non-motor diagnoses.

An accurate diagnosis of PD rests on the clinician’s ability to recognize its characteristic signs and associated symptoms, especially in the early stages.  Optimal management should start at diagnosis, and requires a multidisciplinary team approach, including a growing repertoire of non-pharmacological interventions.

References:

  1. Parkinson J. An Essay on the Shaking Palsy, Sherwood, Neely, and Jones, London 1817.
  2. Bloem, B. R., Okun, M. S., & Klein, C. (2021). Parkinson’s disease. The Lancet, 397(10291), 2284–2303. https://doi.org/10.1016/s0140-6736(21)00218-x
  3. Armstrong MJ, Okun MS.  (2020) Diagnosis and treatment of Parkinson disease: a review. JAMA. 2020; 323: 548-560
  4. Marras C, Tanner CM. Epidemiology of Parkinson’s Disease. In: Movement Disorders: Neurologic Principles and Practice, 2nd ed, Watts RL, Koller WC (Eds), The McGraw-Hill Companies, New York 2004. p.177.
  5. Lang AE, Lozano AM. Parkinson’s disease. First of two parts. N Engl J Med 1998; 339:1044.
  6. Van Den Eeden SK, Tanner CM, Bernstein AL, et al. Incidence of Parkinson’s disease: variation by age, gender, and race/ethnicity. Am J Epidemiol 2003; 157:1015.
  7. Langston JW. The Parkinson’s complex: parkinsonism is just the tip of the iceberg. Ann Neurol 2006; 59:591.
  8. Louis ED, Levy G, Côte LJ, et al. Clinical correlates of action tremor in Parkinson disease. Arch Neurol 2001; 58:1630.
  9. Hoehn MM, Yahr MD. Parkinsonism: onset, progression and mortality. Neurology 1967; 17:427.