Why isn't Parkinson's considered a mental illness if its origin is in the brain?

Parkinson’s, dementia, motor neuron disease, spinal injuries, and neurological injuries are all considered to be disabilities. So is a mental health condition.

The origin of mental illness is not in the brain!

I assume you’re thinking about the unproven chemical imbalance theory big pharma use to justify selling expensive drugs.

Mental illness is a result of genetic and environmental factors.

Some studies may show that people with mental illness have changes in the neurochemistry of their brain.

However, due to our individuality, we all have different brain chemistry.

There’s no such thing as normal or average brain chemistry. We all have unique chemical systems.

Back to your question.

People with the above mentioned disabilities usually develop a mental illness like depression and anxiety. In these circumstances, the correct description of their condition is "Duel Diagnosis", Co-occurring conditions", and Comorbidity".

We make up the above terms so that professions, patients and carers can communicate or speak the same language when discussing a person's condition.

Are reasons why it's useful to make up the jargon is for research purposes and diagnostic reliability.

Reference: Kamal Bekhazi