Parkinson’s Disease which is sometime called Parkinson’s or PD is a movement disorder where the dopamine-producing neurons in the substantia nigra of the brain undergo degeneration. Parkinson’s is one of the most common neurological disorder. It’s a progressive adult onset disease and it gets more common with age.
Most of the time there’s no known cause but in a few cases there might be a genetic cause like mutation in the PINK 1, PARKIN or Alpha SYNUCLEIN genes and in rare cases Parkinsonism symptoms might be caused by MPTP, a toxic impurity that can be found in the recreational drug MPPP which is a synthetic opioid.
Role of substantia nigra:-
No matter what the cause is, Parkinson’s derived from the death of dopamine producing or dopaminergic neurons in the substantia nigra. The name substantia nigra means black substance (substantia – substance, nigra – black) since it’s darken than other brain regions when we look at a slice of the brain on an autopsy. There are two substantia nigra present in the brain on each side of midbrain. The substantia nigra is a part of the basal ganglia which is a collection of brain regions that contribute movement through their connections with a motor cortex. In Parkinson’s disease, these darken areas of substantia nigra gradually disappear. Under a microscope, Lewd bodies which are eosinophils round inclusions made of alpha-synuclein protein are present in the affected substantia nigra neurons before they die.
The substantia nigra can be split into two sub regions. First, there is the pars reticulate which receives signals from another part of the basal ganglia called a Striatum which is a term for the caudate and putamen put together and relays messages to the thalamus via neurons rich in the neurotransmitter GABA also known as Gamma-aminobutyric acid. Second, there’s the pats compacts and this is the part of substantia nigra affected in Parkinson’s. The pars compacta sends messages to the striatum via neurons rich in the neurotransmitter dopamine forming the Nigrostriatal pathway which helps to stimulate the cerebral cortex and initiate movement. Therefore when substantia nigra’s pars compacta neurons die the individual might be in a Hypokinetic or a low movement state which is commonly seen in Parkinson’s.
Clinical Features:-
1) Tremor – It is an involuntary shakiness most noticeable in the hands characteristically called a Pill rolling tremor because it looks like someone rolling a pill between their thumb and index finger. This is a resting tremor means it present at rest and diminishes with intentional movement.
2) Rigidity – There are a series of catches or stalls as a person’s arms or legs are passively moved by someone else. It is also responsible for the stooped posture and in almost expressionless face.
3) Bradykinesia – It is slow movement or hypokinesia which is less in movement and Akinesia which is an absence of movement and all these result from difficulty initiating movement (leg freeze up with a shuffling gait or small steps )
4) Postural Instability – It causes problems with balance and can lead to falls.
Non motor functions can be affected in Parkinson’s as well leading to additional common symptoms including:-
1) Depression
2) Dementia
3) Sleep Disturbance
4) Difficulty in Smelling