September 6, 2016

Peripheral Neuropathy and Parkinson's and Me

When I was diagnosed with Parkinson's disease (PD) in September 2009, my doctor prescribed the gold standard med -- carbidopa-levodopa (brand name Sinemet).

At first, I took two pills of the regular carbidopa-levodopa 25-100 three times a day, and the dosage has increased several times since then. Now, I take two pills of the extended release carbidopa-levodopa 25-100 seven times a day.

My disease no doubt will continue to progress, but I’ve reached the maximum recommended dosage of the drug. Recently, I've noticed that the Sinemet isn’t working like it used to. My "off periods" between doses have increased, and I certainly don’t walk as well as I did six months ago.

In addition, I'm having more frequent incidents of orthostatic hypotension and strange flare-ups of incontinence. Washington’s summer heat and humidity bother me more than ever, and -- for the first time -- I'm experiencing occasional bouts of depression.

I'm not a happy camper. Questions abound.

Is some of my malaise due to the lingering effects of my shingles attack? Since I’ve clearly had PD for at least ten years, are these troubling developments simply signs that the disease is moving into its final stages? 

Are things going on that my doctors and I haven’t yet identified?

Peripheral Neuropathy
That last question brings me to today’s topic. In rereading some of my medical records, I was reminded that one of my PD doctors had wondered whether I was experiencing peripheral neuropathy (PN) in addition to Parkinson's disease.

A Google search on PN produced this info from the Mayo Clinic:
If autonomic nerves are affected, signs and symptoms might include:
  • Heat intolerance and altered sweating
  • Bowel, bladder or digestive problems
  • Changes in blood pressure, causing dizziness or lightheadedness
I certainly recognize those bullet points.

PN and PD
When I Googled "peripheral neuropathy" and "Parkinson's disease" one of the hits led to a research paper that ended with this comment:
This intriguing study demonstrates a somewhat unexpectedly high prevalence of PN in IPD patients and cites an association with elevated MMA levels, perhaps mediated by exposure to L-dopa. L-dopa may indeed interact with methylation pathways involved in folate metabolism, providing a mechanism for MMA elevation. Although causation is not proven here, if verified, this study may change the way we care for patients with IPD. PN in IPD could substantially contribute to gait disturbance and disability in some patients with IPD, and prevention of PN would be an important advance. Exposure to L-dopa is inevitable in most IPD patients at some point during their course, but perhaps we should be measuring MMA levels in these patients and treating with cobalamin supplementation to reduce MMA levels and prevent neuropathy. Further studies, including treatment trials, seem warranted.

Clinicians use MMA levels to detect vitamin B12 deficiencies.

What’s Next?
I relayed this information to my neurologist. As a result, I’ll soon be tested for peripheral neuropathy. Just before my shingles attack this spring, I had two blood tests. I have a funny feeling that my experience with the virus may have messed things up, so I’ll get another blood test soon.

In recent research, I’ve also read that PD and/or carbidopa can actually cause vitamin deficiencies.

Stay tuned.

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