I hope I'm not stirring the pot too much-- I haven't been diagnosed with anything yet, just having a lot of symptoms that are scary (to me.) and trying to gather the courage to pursue a diagnosis. I found this article from Medscape Today that mentions a phenomenon similar to 'cogwheeling rigidity' that can exist with essential tremor as well. It's important to differentiate between the two:

Here's the text since I can't post a link yet-

"Because essential tremor and parkinsonian tremor are two common and chronic forms of pathologic tremor, it is important to be able to differentiate them ( Table 5 ). In many patients with essential tremor, a palpable, cogwheel-like, upper limb tremor may be detected, especially with voluntary, repetitive motion of the contralateral limb. This phenomenon (Froment sign) should not be mistaken for the cogwheel-like rigidity of parkinsonism."