Overview
Parkinson’s Disease is a neuropsychological disorder characterised by neurocognitive impairments. These impairments usually start around 60 years of age and get progressively worse over time.
Neurocognitive degeneration can be seen when the person has difficulties in attention span, exhibits executive dysfunction, learning and memory, social cognition, etc.
In Parkinson’s disease, deficits can be seen in executive functioning and motor functioning. Executive functioning includes information processing speed, organisation of information and planning.
The motor functioning in Parkinson’s is affected at least a year before cognitive decline. Motor functioning deficits can be seen in the form of tremors initially.
But move onto stiffness and slowing movement (bradykinesia) at later stages. As the disease progresses, symptoms get worse. Balance may be affected and the person starts stooping.
The automatic movements such as eye blinking, smiling, swinging of arms while walking are also slowed. Speech may be affected in ways such that it may lack tonal differences. It may be soft, hurried or slurred.
In Parkinson’s, the deficits can be major or mild. This distinction is based on the impairment and the level of assistance required for the person to carry out day to day activities.
Major deficits mean greater impairment and assistance with most basic day to day activities while mild deficits mean lesser assistance and the person can carry out basic day to day activities.
The research reporting the causes of Parkinson’s Disease is quite sparse. Not much is known about the origin of the disease.
Parkinson’s is a sporadic onset of neuronal degeneration which is caused due to decreased dopamine levels. Certain gene mutations have been identified as the cause of Parkinson’s.
However, these aren’t found in all patients of Parkinson’s Disease and more research for the same is warranted.
DSM-5 notes exposure to various environmental chemicals such as pesticides and certain toxins as a risk factor for acquiring Parkinson’s, but the rates of such an occurrence are quite low.
Parkinson’s is also related with Lewy Bodies, which are clumps of substances found in the brain cells of people with Parkinson’s Disease.
This disorder usually starts in the 60s and affects the nervous system. The person exhibits cognitive difficulties, constipation due to slowed digestion process, changing moods, apathy and irritability.
Since movements are slowed, slowed swallowing, chewing and eating can be seen causing the person to drool. Sleep habits are also affected and may cause Rapid Eye Movement Sleep Behaviour Disorder.
Common Signs and Symptoms
Common Signs and Symptoms include:
- Mood alterations causing depression, irritability or apathy.
- Motor dysfunction is seen as slowed voluntary movements known as bradykinesia or slowing of automatic movements such as blinking, swinging of hands while walking, etc.
- Stooped posture and balance issues.
- Difficulty swallowing food, chewing and eating slowly, drooling.
- Constipation.
- Cognitive impairments where a person has difficulty planning, organising and processing information.
- In severe cases, they may need assistance with day to day activities.
Risk Factors
Parkinson’s Disease affects males more than it affects females. The reason for this is unknown.
DSM-5 notes genetic and environmental factors contributing to the onset of Parkinson’s Disease. Several genetic mutations are linked to the earlier and later onset of Parkinson’s Disease.
Mutations on SNCA which makes alpha-synuclein protein are seen in Parkison’s disease. This protein is seen in clumps on individual brain cells of patients with this disease.
Mutations of genes named PARK7 and PINK1 are related to mitochondrial stress and protection of mitochondria are seen to be malfunctioning causing early onset of Parkinson’s Disease.
Mutations in LRRK2 cause late onset of the disease. Mutations of PARK2, which is responsible for breaking down and recycling protein, is also linked with onset of Parkinson’s Disease.
DSM-5 notes exposure to certain toxins and pesticides is linked to the onset of Parkinson’s disease.
Diagnosis
Diagnosis for this disorder is generally given by a neuropsychologist, neuropsychiatrist or a neurologist.
Performance on neuropsychological test batteries as well as clinical examinations of cognitive functions is carried out to determine the severity of the disorder.
Brain imaging and cerebrospinal fluid testing are some medical procedures associated with the diagnosis of Parkinson’s. Some people may opt for gene testing especially if there is a strong family history of developing Parkinson’s Disease.
Ancillary and olfactory testing, Dopamine Transporter Scan, also known as DaTScan may be carried out to confirm the diagnosis.
To be diagnosed with Parkinson’s Disease, following criteria must be met:
- Neurocognitive dysfunction characterised by problems in executive functioning, language and memory. There may be hallucinations and delirium.
- Speech related issues.
- Motor dysfunction characterised by bradykinesia, loss of automatic movements, balance and posture issues, digestion issues, etc.
- Mood alterations causing depression, irritability or apathy.
Neuropsychologists are required to rule out other medical conditions or substance use that may cause similar symptoms.
Treatment
There is no cure for Parkinson’s Disease. However, symptomatic treatment is available.
Parkinson is generally caused due to loss of dopaminergic neurons. Several studies have indicated that it is a gradual process affecting the brain stem and olfactory regions of the brain and progressing towards the cortical areas.
The cognitive deficits, although varying in degree of severity, do not show up until the disease doesn’t progress into 70-80% cell loss. Hence, it is highly recommended that neuro biomarkers in vulnerable populations be tracked at a regular rate.
Since Parkinson’s is caused due to dopaminergic cell loss. Pharmacological treatment is often directed towards increasing levels of dopamine. Since dopamine cannot be administered directly, medication that mimics the same effect or inhibits dopamine oxidative metabolism may be administered.
Levodopa is one of the most effective medications for the treatment of Parkinson’s Disease. It can be administered orally or needs to be paired up with other substances such as carbidopa which sustains the release of dopamine until it reaches the right receptor sites.
Side effects include feeling lightheaded and sometimes, nausea. Duopa, gel based, is another medication of the same levodopa group administered using a tube where the medication is pumped into the intestines of the patient.
Other medication includes dopamine agonists that mimic dopamine release in the system.
This group includes pergolide, pramipexole dihydrochloride, ropinirole hydrochloride, rotigotine, and apomorphine hydrochloride. They often come with a host of side effects such as hypersexuality, sleep disturbances, gambling, etc.
MAOA and MAOB (Monoamine Oxidase isoforms) inhibitors, entacapone and opicapone are also administered. These drugs inhibit the MAO receptors and decrease the breakdown of dopamine, preventing cell loss.
Non pharmacologic treatments include Deep Brain Stimulation and Gene Therapy. In the Deep Brain Stimulation surgery, electrodes are placed on the brain connected to a pacemaker like device.
This device is connected to the electrodes with wires under the skin. The electrodes stimulate the neuron cells in the brain helping it release certain chemicals. This method has shown results in the treatment of Parkinson’s.
In Gene Therapy, adeno-associated viral vectors carrying the human aromatic amino acid decarboxylase (AADC) gene are delivered in the subthalamic nucleus and putamen neurons of the patient’s brain.
This prevents dopamine loss administered via levodopa therapy.
Similarly, glutamic acid decarboxylase (GAD), glial cell line-derived neurotrophic factor (GDNF) and Neurturin gene are being investigated for gene therapy for the treatment of Parkinson’s Disease.
Differential Diagnosis
1. Major or mild neurocognitive disorder with Lewy bodies: This distinction is based on the timing and sequence of motor and cognitive symptoms. For NCD to be attributed to Parkinson’s disease, the motor and other symptoms of Parkinson’s disease must be present well before (at least 1 year prior) cognitive decline has reached the level of major NCD, whereas in major or mild NCD with Lewy bodies, cognitive symptoms begin shortly before, or concurrent with, motor symptoms.
2. Major or mild neurocognitive disorder due to Alzheimer’s disease: The motor features are the key to distinguishing major or mild NCD due to Parkinson’s disease from major or mild NCD due to Alzheimer’s disease. However, the two disorders can co-occur.
3. Major or mild vascular neurocognitive disorder: Major or mild vascular NCD may present with parkinsonian features such as psychomotor slowing that may occur as a consequence of subcortical small vessel disease. However, the parkinsonian features typically are not sufficient for a diagnosis of Parkinson’s disease, and the course of the NCD usually has a clear association with cerebrovascular changes.
4. Neurocognitive disorder due to another medical condition: When a diagnosis of major or mild NCD due to Parkinson’s disease is being considered, the distinction must also be made from other brain disorders, such as progressive supranuclear palsy, corticobasal degeneration, multiple system atrophy, tumors, and hydrocephalus.
5. Neuroleptic-induced parkinsonism: Neuroleptic-induced parkinsonism can occur in individuals with other NCDs, particularly when dopamine-blocking drugs are prescribed for the behavioral manifestations of such disorders
6. Other medical conditions: Delirium and NCDs due to side effects of dopamine-blocking drugs and other medical conditions (e.g., sedation or impaired cognition, severe hypothyroidism, Bi2 deficiency) must also be ruled out.
Comorbidity
Parkinson’s disease is comorbid with Alzheimer’s disease, cerebrovascular disease, depression and apathy.
Specialist
A neurologist, neuropsychologist, or neuropsychiatrist is often referred to for treatment.
