Rapid Progression and autoimmune disease

I was diagnosed in October with Parkinsons following a SPECT and PET scan.
It has progressed very rapidly. I unable to walk more than about twenty steps, l sleep about half of the day and feel unable to carry out tasks around the house. I generally feel very unwell. My neurologist sees me once a month and is shocked by how quickly things have worsened for me.
I also have autoimmune encephalitis and wonder if the two could be linked. I am not currently having treatment for the autoimmune encephalitis. I am steroid resistant so have always been treated with IVIG. The last infusion was in November 2024.