Second Most Common Neurodegenerative Disorder: Parkinson's Disease

Introduction

Parkinson’s disease (PD), the second most common neurodegenerative disorder after Alzheimer’s disease, was originally described in 1817 by James Parkinson in the classic ‘‘Essay on the Shaking Palsy’’. Idiopathic Parkinson’s disease (PD) still has a lot to be uncovered. Rapidly aging populations, with increasing life expectancies, suggest PD will become an even bigger health problem in the near future. Most cases are sporadic, although there are some clearly defined families with autosomal dominant inheritance patterns. Most of these families are containing defective genes for one of several intracellular proteins. The ultimate pathology in PD is the presence of Lewy bodies (ubiquitin-containing granules) in the cytoplasm of neurons in the degenerating substantia nigra, pars compacta (the region of dopaminergic neurons projecting to the substantia nigra). It is characterized by cell degeneration in the substantia nigra. This causes a disturbance between the neurotransmitters dopamine and acetylcholine, the balance of which enables normal movement.

Signs and symptoms

Symptoms do not develop until about 50–60% of the nigral neurons are lost and about 80–85% of the dopamine content of the striatum is depleted. The symptoms can include tremors, rigidity and postural problems, excessive perspiration, gastrointestinal difficulties, weight loss, fatigue, pain, problems with sexual function, and incontinence. A decline in cognitive function, dementia, and depression have also been reported. The symptoms can affect functional performance. Medication can lead to the on/off phenomenon, with symptoms worsening as the medication fails to have the desired effect. The presence of additional health difficulties further diversifies the experience of Parkinson’s disease.

Four separate major groups of symptoms are usually described as part of the symptom complex of parkinsonism. These groups include tremor, rigidity of the muscles, akinesia, and loss of normal postural fixing reflexes.4 The degree to which each of these four signs occurs in parkinsonism varies considerably from patient to patient.

The tremor consists of the rhythmically alternating contraction of a given muscle group and of its antagonists.4 The rate of tremor averages about two to six oscillations per second and is usually more obvious in the distal parts of the limbs than in proximal parts. The tremor, however, does not only affect the limbs but also in some cases the jaw, tongue, face, and pectoral structures.

The rigidity of the muscles is another major constituent of Parkinson's disease. The associated rigidity in Parkinson's cases is generally an impedance to passive movement present throughout the integral range of motion, thereby serving to differentiate rigidity from spasticity. When the intensity of the rigidity is similar thoroughly the range of motion, the rigidity is called 'lead-pipe' rigidity. In some Parkinson's cases, nonetheless, the hypertonic muscles when passively stretched exhibit an irregular jerkiness in resisting the movement as if they were being pulled across a ratchet, a condition referred to as 'cog-wheel' rigidity. Rigidity may be the initial symptom of Parkinson's disease in some patients.

Although tremor at rest is the most dramatic symptom of Parkinson's disease, the most disabling symptom of the condition is akinesia. The term 'akinesia', when taken generally, refers to three related symptoms: 

1. marked poverty of spontaneous movements; 
2. loss of normal associated movements (e.g. loss of arm swing during walking); 
3. slowness in the initiation and execution of all voluntary movements. 

Overall akinesia is manifest clinically in signs, such as a 'mask-like' facial expression and a reduction in a wide variety of spontaneous movements seen in normal individuals.

Postural fixation reflexes are those reflexes that cause sufficient muscular contractions to support part of the body to maintain a particular posture. The postural fixation of the head of Parkinson's patients is often abnormal such that the affected individual's head may fall forward while the patient is in an upright position. Persons with Parkinson's disease may also have problems with postural fixation of the trunk so that they may be unable to maintain an upright position while seated, standing, or walking.

Other manifestations include psychiatric symptoms such as anxiety and depression and dysautonomic symptoms such as hypotension and constipation, paresthesias, cramps, olfactory dysfunction, and seborrheic dermatitis. As the disease progresses, decreased cognitive ability may appear.

References

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3. Koerts J, Konig M, Tucha L, Tucha O. Working capacity of patients with Parkinson’s disease–a systematic review. Parkinsonism Relat Disord. 2016;27:9-24.
4. Boller, F., Mizutani, T., Roessmann, V. and Gambetti, P. (1980) Parkinson's disease, dementia and Alzheimer's disease: Clinicopathological correlations. Annals of Neurology, 7, 329-335.
5. Chenery, H.J., Murdoch, B.E. and Ingram, lC.L. (1988) Studies in Parkinson's disease. I. Perceptual speech analysis. Australian Journal of Human Communication Disorders, 16, 17-29.
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7. Marsden CD. Movement disorders. In :WeatherallDJ,Ledingham JGG, Warrell DA, editors. Oxford textbook of medicine, vol. 3. New York: Oxford University Press Inc.; 1996. p. 3998–4022.