Some diseases are easy to diagnose. Take chickenpox—back in the day, before chickenpox vaccine became popular and case numbers plummeted, I’d see itchy, rashy, feverish kids several times a week during the winter and early spring. The stories were consistent: fevers for a day or two, then came the rash – dozens of small vesicles (thin-walled blebs filled with a watery fluid), each one on a red base.* 

I’d typically see the kids about 4 days into the rash, when the fevers and itchiness were driving everyone batty. I’d check for secondary bacterial infections and we’d discuss comfort measures that can make waiting out the illness less awful for both sick child and sleep-craving parent. Barring any unusual complications, things were better in a few days, and the scabby young victim now had lifelong immunity. Easy diagnosis, predictable stuff.

You might be tempted to think that Parkinson’s disease would be easy to diagnose too, if you never looked past the opening lines of the Movement Disorder Society’s (MDS) clinical diagnostic criteria (See Table 1):

“The first essential criterion [in diagnosing PD] is parkinsonism, which is defined as bradykinesia  and at least one of these two: a resting tremor or rigidity.” **

• (Bradykinesia is defined as “reduction in speed and amplitude of voluntary movement.” This is much more than just slow walking. It includes such things as tiny handwriting that gets even smaller as the person writes; decreased facial expressiveness; weak voice; less frequent blinking; decreased arm swing when walking; and difficulty with dressing and with turning in bed.)

So, if you’ve got a slow-moving, retired pediatrician with either shaking limbs or unusual stiffness you’re looking at a guy with PD, right?

Not so fast… 

What you’ve got so far is parkinsonism; you haven’t diagnosed Parkinson’s disease – at least not yet. PD is the most common neurologic condition that causes parkinsonism, but it’s far from the only one. So, once you clear the parkinsonism hurdle, you’ve got the rest of the Movement Disorder Society’s diagnostic criteria to consider: Supportive Criteria, Absolute Exclusion Criteria, and Red Flags. (Again, see Table 1. I never said this would be easy…)

Supportive criteria:

These are signs and symptoms that are often found in people with Parkinson’s but are not required to make the diagnosis. They include the effects of taking a “dopaminergic” medication (levodopa, for example)– is there a “clear and dramatic response?” Does the patient experience dyskinesia as a side effect? Other supportive criteria include the loss of the sense of smell and evidence of PD-related heart disease.

Absolute exclusion criteria:

The name says it all. Absolute exclusion criteria can exclude PD from your diagnostic possibilities…absolutely. The criteria include a number of complex neurologic features that would point to other diseases; taking medications that are known to cause parkinsonism (e.g., some seizure medications); not improving despite taking high doses of dopaminergic medications; having a normal PD-related brain scan; and (the neurologist’s wild card) an expert’s opinion that something else is going on.

Red flags: 

These are signs and symptoms that may warn of something other than PD, but aren’t quite definitive in and of themselves. Among them is another batch of complex neurologic signs and symptoms that boil down to this: if your symptoms progress too quickly or too slowly (or not at all); if you fall down or faint a lot; if your symptoms are symmetrical (PD usually affects one side of the body more than the other); or if you’re not having sleep problems, constipation, psychiatric problem, and a host of other non-movement-related symptoms within 5 years of your diagnosis…maybe you don’t have PD after all.

Final score:

If your neurologist finds that you have parkinsonism, plus at least two supportive criteria, and no red flags or absolute exclusion criteria, you’ve got “clinically established PD.” If your supportive criteria exceed your red flags (of which there can be no more than two), you are considered to have “probable PD.” And if you have more than 2 red flags or any absolute exclusion criteria, you most likely have something other than PD. Back to the diagnostic drawing board with ye!

As you can see, it’s complicated. That’s why it can take weeks, months, sometimes even years for a slowly progressive disease like PD to declare itself, and why you really need a neurologist – even better, a neurologist who specializes in movement disorders like PD – to help you get an accurate diagnosis. (Retired pediatrician = not the guy you’re looking for.)

Coming up in the “Parkinson’s – the Basics” series: Now that you’ve got your diagnosis, you may ask yourself, “What is Parkinson’s disease, anyway? And why did I get it?” And the biggest question of all: “What’s next for me?” Answers (or at least some answers) to follow…

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* The classic description of the chickenpox lesion – “a dewdrop on a rose petal” – harkens to a more poetic medical era. A more accurate description: “An unattractive, sometimes yellowish bloblet plopped on a tiny patch of red skin. When it hasn’t been scratched beyond all recognition, that is…” (Copyright: me)

** Sometimes a picture really is worth a thousand words – click on link at bottom for a concise discussion of these three cardinal features of PD:

• Bradykinesia (see in post above)
• Resting tremor: “…slow, regular movements of the hands and sometimes the legs, neck, face, or jaw, when those parts are at rest; the tremor usually stops when that part is voluntarily moved.” 
• Rigidity: “…a stiffness of the arms or legs beyond what would result from normal aging or arthritis. Some people call it ‘tightness’ in their limbs.”
  • There are two main types of rigidity: “lead pipe rigidity,” which presents as a smooth resistance to movement of the limb, and “cogwheel rigidity,” which is a ratchet-like jerkiness superimposed on lead pipe rigidity.

MEDSKL – “Parkinson’s Disease: What You Need to Know